uncle
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A1 noun /ˈʌŋkəl/

uncle

叔叔/舅舅
Meaning
the brother of one's father or mother
Example
My uncle is visiting us next week.
我的叔叔下周会来看我们。
B1 noun /ˈjuːs.fəl.nəs/

Usefulness

有用性
Meaning
the quality of being useful; practical value or helpfulness
Example
The usefulness of this tool became apparent during the project.
这个工具的有用性在项目过程中变得显而易见。
B2 noun /ˈjuː.sɪdʒ/

Usage

使用
Meaning
the action of using something; the way in which words are used in a language
Example
The dictionary explains the correct usage of difficult words.
词典解释了难词的正确用法。
C1 adjective /ˌʌndərˈsteɪtɪd/

understated

低调的
Meaning
Presented in a subtle and restrained way.
Example
She wore an elegant but understated dress.
她穿了一件优雅但低调的裙子。
C2 adjective /ˈʌndjʊləs/

undulous

波浪形的
Meaning
Having a wavy surface or form.
Example
The artist painted the undulous sea at sunset.
艺术家在日落时画了波浪形的海洋。
C2 adjective /ʌnˈsʌlid/

unsullied

无暇
Meaning
not spoiled or made impure; perfectly clean or pure
Example
His reputation remained unsullied despite the accusations.
尽管有指控，他的声誉仍然无暇。
B2 adjective /ʌnˈkwɒl.ɪ.faɪd/

Unqualified

不合格的; 无资格的;
Meaning
not having the necessary skills or qualifications; complete or absolute
Example
He was unqualified for the engineering position due to lack of experience.
他因缺乏经验而不适合这个工程职位。
C2 adjective ˌʌn.əˈseɪ.lə.bəl

unassailable

不可攻破
Meaning
Unable to be attacked, questioned, or defeated.
Example
An unassailable position ensures dominance.
不可攻破的位置确保主导地位。
A1 preposition/conjunction /ʌnˈtɪl/

until

直到
Meaning
up to the time of
Example
I will wait until you come back.
我会等到你回来。
C1 adjective /ʌnˈduː/

Undue

过度的; 不适当的; 超过必要或适当的
Meaning
excessive; inappropriate; more than is necessary or proper
Example
The teacher complained about undue pressure from parents.
老师抱怨家长施加的过度压力。
C1 noun /ˈʌndərˌteɪkər/

undertaker

殡葬员
Meaning
A person whose job is to prepare the dead for burial and arrange funerals.
Example
The undertaker prepared the body for the funeral service.
殡葬员为葬礼服务准备了尸体。
C1 adjective /ʌnˈsiːmli/

unseemly

不得体
Meaning
Not proper or appropriate in behavior or appearance; unbecoming.
Example
His unseemly remarks embarrassed everyone at the dinner table.
他不得体的言论让晚餐桌上的每个人都感到尴尬。
A2 adjective /ʌnˈtaɪdi/

Untidy

凌乱的; 无序的;
Meaning
not neat or orderly; messy and disorganized
Example
Her untidy room was filled with clothes scattered everywhere.
她凌乱的房间充满了四处散落的衣服。
C2 adjective /ˌʌnəˈʃʊəd/

unassured

不确定的
Meaning
Lacking confidence or certainty.
Example
She gave an unassured answer during the interview.
她在面试中给出了一个不确定的答案。
B1 adjective /ˈjuːnɪfɔːrm/

Uniform

制服
Meaning
consistent; identical; standardized
Example
All students must wear a uniform to school.
所有学生必须穿制服上学。
B1 adjective /ˌʌnˈɪntrəstɪŋ/

uninteresting

无趣的
Meaning
not holding attention or curiosity; boring
Example
The lecture was uninteresting and difficult to stay focused on.
这次讲座很无趣，很难集中注意力。
C2 adjective /ʌnˈælɔɪd/

unalloyed

纯净
Meaning
Pure, complete, and not mixed with anything else.
Example
She felt unalloyed joy at the news of her success.
她听到成功的消息时感到纯粹的喜悦。
B1 verb /ˈʌpˌɡreɪd/

upgrade

升级
Meaning
to raise something to a higher standard, improve
Example
We decided to upgrade the software to the latest version.
我们决定将软件升级到最新版本。
C2 noun /ˈʌŋɡwənt/

unguent

药膏
Meaning
A soothing or healing ointment applied to the skin.
Example
The doctor applied an unguent to heal the burn.
医生涂抹了药膏来治愈烧伤。
C2 adverb /ʌnˈɜːrɪŋli/

unerringly

毫无错误
Meaning
Without making any mistakes; always accurate
Example
The archer aimed unerringly at the target.
弓箭手毫无错误地瞄准了目标。
B2 noun /ʌnəˈbɪləti/

unability

无能
Meaning
the state of being unable to do something; incapacity
Example
His unability to solve the problem caused delays in the project.
他解决问题的无能导致了项目的延误。
C1 noun /ˈʌndərˌɡɑːrmənt/

undergarment

内衣
Meaning
a piece of clothing worn under outer clothes, usually next to the skin
Example
He bought new undergarments for the wedding.
他为婚礼买了新的内衣。
C1 adjective ˌʌn.pəˈtɜːbd

unperturbed

不为某事烦恼或困扰；冷静且镇定
Meaning
Not worried or disturbed by something; calm and composed.
Example
She remained unperturbed despite the challenges.
尽管有挑战，她依然保持冷静。
A2 noun /ˈjuːnɪt/

unit

单元
Meaning
an individual thing or person regarded as a single and complete entity
Example
Each unit in the production line is carefully tested.
生产线上的每个单元都经过仔细测试。
C1 noun /ˈʌndərˌwɜːrld/

underworld

地下世界
Meaning
The criminal world of organized crime or the mythical world of the dead.
Example
The detective spent years studying the secrets of the underworld.
侦探花了很多年研究地下世界的秘密。
C1 adjective ʌnˈjiːl.dɪŋ

unyielding

坚定或坚韧
Meaning
Not easily broken or giving in to pressure.
Example
Her unyielding determination helped her overcome all challenges.
她坚定的决心帮助她克服了所有的挑战。
B2 adjective /ˌʌnrɪˈzɒlvd/

unresolved

未解决的
Meaning
not solved or settled; remaining undecided or unclear
Example
The dispute remains unresolved despite several meetings.
尽管开了几次会议，这个争议仍未解决。
C1 adjective /ˌʌnəbˈtruːsɪv/

unobtrusive

不引人注目
Meaning
not attracting attention; blending in without causing notice
Example
The security cameras are designed to be unobtrusive.
安全摄像头被设计成不引人注目。
C1 adjective /ʌnˈmaɪndfəl/

Unmindful

不留心的; 疏忽的;
Meaning
not paying attention; careless; heedless
Example
She was unmindful of the danger around her.
她没有注意到周围的危险。
B2 adjective /ʌnˈtʃeɪndʒəbəl/

Unchangeable

不可改变的; 固定的;
Meaning
not able to be changed or altered; fixed and permanent
Example
The laws of physics are unchangeable principles that govern the universe.
物理法则是不变的原则，支配着宇宙。
B2 adjective /ʌnˈberəbəl/

Unbearable

无法忍受
Meaning
too painful, annoying, or unpleasant to tolerate; impossible to endure
Example
The heat in the desert was unbearable.
沙漠中的热度是无法忍受的。
B2 adjective /ˌʌndɪˈveləpt/

Undeveloped

未开发的; 未成熟的; 原始的
Meaning
not yet developed; immature or primitive
Example
The undeveloped land was later turned into a park.
未开发的土地后来被改建成了一个公园。
B2 adjective /ˌʌnəˈfɪʃ.əl/

Unofficial

非官方的
Meaning
not officially authorized or confirmed; informal
Example
The unofficial results showed a close race.
非官方的结果显示出一场激烈的比赛。
C2 adjective /ʌkˈsɔːriəs/

uxorious

过度宠爱妻子
Meaning
excessively fond of or submissive to one's wife
Example
He was so uxorious that he agreed with everything his wife said.
他是如此的宠爱妻子，以至于同意了妻子说的每一件事。
C1 adjective /ʌnˈtʃælɪndʒd/

Unchallenged

无可争议的; 被接受的没有反对; 没有对手
Meaning
not disputed or questioned; accepted without opposition; having no rival
Example
He remained the unchallenged champion for five years.
他五年保持不败的冠军。
C1 adjective /ʌnˈɡɑː.dɪd/

Unguarded

不设防的
Meaning
not protected or defended; careless about revealing private thoughts or information
Example
In an unguarded moment, she revealed her true feelings about the project.
在一个不设防的时刻，她揭示了她对这个项目的真实感受。
C1 noun /ˈʌlsər/

ulcer

Meaning
a sore on the skin or a mucous membrane that does not heal easily
Example
The doctor prescribed medicine to treat the stomach ulcer.
C1 adjective /ʌnˈtaɪərɪŋ/

Untiring

不知疲倦的; 坚持不懈的; 永不止步的
Meaning
continuing without stopping; persistent; tireless
Example
Her untiring efforts finally led to success.
她的不知疲倦的努力最终带来了成功。
A1 interjection /ʌ/

uh

呃
Meaning
a sound people make when they hesitate or are unsure what to say next.
Example
Uh, I’m not sure if that’s the right answer.
呃，我不确定这是不是正确的答案。
C1 adjective /ʌnˈspiːkəbl/

unspeakable

难以形容
Meaning
too bad or shocking to be expressed in words
Example
The survivors endured unspeakable horrors during the war.
幸存者在战争中忍受了难以形容的恐怖。
C1 noun /ˌʌl.tɪˈmeɪ.təm/

Ultimatum

最后通牒
Meaning
a final demand or statement of terms, the rejection of which will result in retaliation
Example
The boss gave him an ultimatum: improve or be fired.
老板给了他一个最后通牒：要么改进，要么被解雇。
C1 adjective /ˌʌnɪmˈplɔɪəbəl/

unemployable

不适合就业
Meaning
Not able to be employed; lacking the skills or qualities necessary for employment
Example
Due to his criminal record, he was considered unemployable in most companies.
由于他的犯罪记录，他在大多数公司被认为是不适合就业。
C1 adjective /ˌʌnəˈkaʊntəbl/

unaccountable

无法解释
Meaning
Not able to be explained or justified.
Example
She felt an unaccountable fear as she entered the dark room.
她进入黑暗的房间时感到无法解释的恐惧。
B2 adjective /ʌnˈendɪŋ/

Unending

无尽的
Meaning
continuing forever; without end
Example
The unending rain made the day feel gloomy.
无尽的雨让这一天显得阴沉。
B1 adjective /ˌʌnɪmˈpɔːrtənt/

unimportant

不重要的
Meaning
not having much value, significance, or influence
Example
The detail seemed unimportant compared to the main issue.
与主要问题相比，这个细节显得不重要。
C1 noun /ˈʌp.tɜːn/

upturn

改善
Meaning
An improvement or upward trend in a situation, especially in business or economy.
Example
The company experienced an upturn in sales last quarter.
该公司在上个季度销售情况有所改善。
A2 adjective /ʌnˈhel.θi/

Unhealthy

不健康的; 有害的
Meaning
harmful to health; not in good health; detrimental to well-being
Example
Eating too much fast food is unhealthy for your body.
吃太多快餐对你的身体不健康。
C2 verb /juˈzɜrp/

usurp

篡位
Meaning
to take someone's position of power illegally or by force
Example
The general tried to usurp the king's throne.
将军试图篡夺国王的王位。
A2 verb /ʌpˈset/

upset

烦扰
Meaning
to make someone worried, sad, or angry; to disturb
Example
The bad news upset everyone.
坏消息 upset 每个人。
B2 adjective /ʌnˈɡreɪt.fəl/

Ungrateful

忘恩负义
Meaning
not feeling or showing thanks for something done or given; not appreciating kindness
Example
She felt he was ungrateful for all the help she had given him.
她觉得他对她给予的所有帮助都忘恩负义。
B1 adjective /ˌʌnɪkˈspektɪd/

Unexpected

出乎意料的; 令人惊讶的
Meaning
not expected or anticipated; surprising
Example
The unexpected news left everyone speechless.
出乎意料的消息让所有人都哑口无言。
B2 adjective /ʌnˈkɒmən/

uncommon

不常见
Meaning
rare, unusual, or remarkable
Example
It is uncommon to see snow in this region.
在这个地区看到雪是不常见的。
B2 adjective /ʌnˈtʃeɪndʒɪŋ/

unchanging

不变的
Meaning
remaining the same over time; not changing
Example
Her love for her family was unchanging throughout the years.
她对家人的爱多年来始终不变。
C2 noun /ˈʌp.wel.ɪŋ/

upwelling

上升流
Meaning
An oceanographic phenomenon that involves wind-driven motion of dense, cooler, and nutrient-rich water towards the ocean surface.
Example
Upwelling brings nutrients to the ocean surface.
上升流将营养物质带到海洋表面。
B2 adverb /ʌnˈdaʊtɪdli/

undoubtedly

毫无疑问
Meaning
without a doubt, certainly
Example
He is undoubtedly the best player on the team.
他毫无疑问是队里最好的球员。
C1 adjective /ˌʌnprɪˈtɛnʃəs/

unpretentious

谦虚的
Meaning
modest; not attempting to impress others with appearance or importance
Example
She lives in an unpretentious home but is very happy.
她住在一个谦虚的家里，但非常快乐。
C1 adjective /ʌnˈsəʊʃəl/

unsocial

不合群的
Meaning
not enjoying the company of others; avoiding social interaction; contrary to social norms
Example
He prefers unsocial hours so he can work alone without interruptions.
他更喜欢不合群的工作时间来独自工作。
B2 adjective ʌnˈprɛsɪˌdɛntɪd

unprecedented

前所未有
Meaning
Never done or known before; without previous example.
Example
Unprecedented advancements in science changed human lives.
科学上的前所未有的进展改变了人类的生活。
B2 adjective /ˌʌnˈkɔːrdɪneɪtɪd/

uncoordinated

不协调; 笨拙
Meaning
lacking coordination, not well-organized or clumsy in movement
Example
His movements were uncoordinated, making him prone to accidents.
他的动作不协调，使他容易发生意外。
C1 noun /ˈʌndərdɒɡ/

underdog

逆袭者
Meaning
a competitor thought to have little chance of winning; a weaker party in a contest
Example
The underdog team surprised everyone by winning the championship.
逆袭者队伍通过赢得锦标赛让所有人都惊讶。
B1 adjective /ˌʌndərˈstændəbl/

understandable

可以理解的
Meaning
Able to be understood; reasonable or justifiable.
Example
Her reaction was understandable given the situation.
考虑到情况，她的反应是可以理解的。
C2 adjective /juːˈnɪsənənt/

unisonant

和谐的
Meaning
Sounding together or in harmony.
Example
The unisonant voices created a powerful effect.
和谐的声音创造了强大的效果。
B1 adjective /ʌnˈjuː.ʒu.əl/

Unusual

不寻常; 奇怪;
Meaning
not typical; strange; different from what is normal
Example
She wore an unusual dress to the party.
她穿了一件不寻常的衣服去参加派对。
B2 noun /ˈʌndərkləʊðz/

underclothes

内衣
Meaning
Clothing worn beneath outer clothes, such as underwear or lingerie
Example
He folded his underclothes neatly before packing them.
他在打包前把内衣叠得整整齐齐。
B2 adjective /ˌʌnrɪˈlaɪəbl/

Unreliable

不可靠的; 不能被信任或依赖
Meaning
not dependable; not able to be trusted or relied upon
Example
The old car is unreliable and breaks down frequently.
这辆老车不可靠，常常坏掉。
C2 adjective /ʌnəˈpiːzd/

unappeased

不平息的
Meaning
Not satisfied or calmed; still feeling discontent or anger
Example
Despite the apology, she remained unappeased.
尽管道歉，她仍然不平息的。
C2 adjective /ʌnˈtʃeɪst/

Unchaste

不道德的; 不纯洁的;
Meaning
not celibate; having engaged in sexual relations; lacking moral purity
Example
The conservative society considered her behavior unchaste and improper.
保守的社会认为她的行为不道德和不合适。
C1 adjective /ʌnˈsəʊʃəbl/

unsociable

不合群的
Meaning
not enjoying the company of others; avoiding social interaction
Example
He became unsociable after moving to a new city.
搬到新城市后，他变得不合群。
C1 adjective /ʌnˈθɪŋkɪŋ/

unthinking

欠考虑的
Meaning
done without careful thought; automatic or thoughtless
Example
His unthinking remark hurt her feelings.
他欠考虑的评论伤害了她的感情。
B2 noun /ˈʌndərˌteɪkɪŋ/

undertaking

事业
Meaning
A task, project, or responsibility that someone agrees to do.
Example
Starting a new company is a difficult undertaking.
创办新公司是一项艰巨的事业。
C1 adjective /ʌnˈbraɪdld/

unbridled

无法控制的
Meaning
Uncontrolled and unrestrained.
Example
The protesters showed unbridled enthusiasm for change.
抗议者展示了对改变的无法抑制的热情。
C1 adjective /ʌnˈsteɪtɪd/

unstated

未声明
Meaning
not expressed directly in words; implied or left unsaid
Example
The contract included several unstated expectations.
合同包括了几个未声明的期望。
B2 adjective /ˈʌt.ɚ/

Utter

完全的; 绝对的; 全部的
Meaning
complete; absolute; total
Example
The movie was an utter disaster at the box office.
这部电影在票房上完全失败了。
B1 adjective /ʌnˈwel/

Unwell

不舒服; 生病
Meaning
not in good health; feeling sick or ill
Example
She has been feeling unwell since yesterday.
她从昨天开始感到不舒服。
B2 verb /ʌnˈkʌvə(r)/

uncover

揭示
Meaning
to reveal something that was hidden or secret
Example
The investigation uncovered new evidence.
调查揭示了新的证据。
C1 noun /ʌnˈfeɪθfʊlnəs/

unfaithfulness

不忠
Meaning
the quality of being disloyal or not faithful; breach of trust or fidelity
Example
His unfaithfulness led to the end of their marriage.
他的不忠导致了他们婚姻的结束。
B1 verb /ʌnˈræp/

unwrap

拆开
Meaning
remove wrapping or covering from something; reveal something gradually or clearly
Example
She carefully unwrapped the gift with excitement.
她兴奋地小心拆开了礼物。
B1 adjective ʌnˈplænd

unplanned

未计划的
Meaning
Not planned or arranged in advance; happening spontaneously without preparation.
Example
Unplanned urbanization contributes to environmental issues.
无计划的城市化会加剧环境问题。
C2 adjective /ˈʌndjʊleɪtɪŋ/

undulating

波动的
Meaning
Having a smoothly rising and falling form or motion like waves.
Example
We drove through undulating hills.
我们驱车穿过起伏的山丘。
C1 adverb /ˌʌnkənˈvɛnʃənəli/

unconventionally

非传统地
Meaning
in a way that is not based on or conforming to accepted standards or norms
Example
She dresses unconventionally, mixing bold colors and patterns that surprise everyone.
她穿着非传统地，混搭大胆的颜色和图案，让每个人都感到惊讶。
B2 adjective /ʌnˈstɛdi/

unsteady

不稳定的
Meaning
not firm or stable; likely to change or fail
Example
She felt unsteady on her feet after the long journey.
长途旅行后，她感到站立不稳。
B1 adjective /ʌnˈlaɪkli/

Unlikely

不太可能; 不大可能
Meaning
not likely to happen; improbable
Example
It's unlikely to rain today with such clear skies.
今天晴空万里，几乎不可能下雨。
C1 adjective /juːˈbɪkwɪtəs/

ubiquitous

无处不在
Meaning
Existing or being everywhere at the same time.
Example
Social media has become ubiquitous among young people.
社交媒体在年轻人中变得无处不在。
C1 adjective /ˌjuːtɪlɪˈtɛəriən/

utilitarian

Meaning
Designed to be useful or practical rather than attractive; relating to the doctrine that actions are right if they are useful or for the benefit of a majority.
Example
The building had a simple utilitarian design.
B1 verb /ʌnˈpæk/

unpack

拆开
Meaning
to remove items from a container; to explain or analyze something in detail
Example
After arriving home, she began to unpack her suitcase.
到家后，她开始拆开自己的行李箱。
C1 adjective /ʌnˈsaɪtli/

unsightly

难看
Meaning
Unpleasant to look at; ugly.
Example
The garbage pile created an unsightly view in the park.
垃圾堆在公园里创造了一个难看的景象。
B2 adjective /ʌnˈwɪl.ɪŋ/

Unwilling

不愿意的; 不情愿的;
Meaning
not ready to do something; reluctant; not wanting to do
Example
He was unwilling to share his secret with anyone.
他不愿意与任何人分享他的秘密。
C1 adjective /ʌnˈtaɪmli/

Untimely

不合时宜
Meaning
happening at an inappropriate or inconvenient time; premature
Example
His untimely death at the age of thirty shocked everyone.
他的过早死亡在30岁时震惊了所有人。
C1 adjective /ʌnˈruːli/

Unruly

不守规矩的; 乱七八糟的;
Meaning
difficult to control or manage; disorderly and disruptive
Example
The unruly crowd refused to follow the safety instructions.
那群无法控制的人群拒绝遵循安全指令。
C1 adjective /ʌnˈɜːrθli/

unearthly

超自然的
Meaning
Strange or unnatural in a way that seems not of this world
Example
The forest was filled with an unearthly glow.
森林中充满了超自然的光辉。
C1 verb /ʌpˈruːt/

uproot

拔除
Meaning
To pull something out of the ground; to remove or displace completely.
Example
They uprooted the old tree from the garden.
他们从花园里把老树拔了出来。
B2 adjective /ʌnˈdɪvaɪdɪd/

Undivided

完整的; 完全的; 不分开或不分裂
Meaning
whole; complete; not separated or split
Example
The team showed undivided attention to the coach's instructions.
团队对教练的指示表现出了完整的注意力。
C1 adjective /ʌnˈhoʊli/

Unholy

亵渎的; 罪恶的; 亵渎的
Meaning
wicked; sinful; profane
Example
The unholy alliance between the two companies caused public outrage.
这两家公司之间的不圣洁联盟引发了公众愤怒。
C2 verb /ʌnˈɑːrm/

unarm

解除武装
Meaning
to remove weapons from someone or to deprive of means of attack or defense
Example
The soldiers were ordered to unarm the prisoners.
士兵接到命令解除囚犯的武装。
B2 verb ˈjuːnɪfaɪ

unify

统一
Meaning
To make or become united, uniform, or whole; to bring together into a single unit.
Example
Adolescents unify with peers for social acceptance.
青少年为了社会接纳与同伴统一。
C2 adjective /ˌʌnɪmˈpiːtʃəbl/

unimpeachable

无可指摘
Meaning
Not able to be doubted, questioned, or criticized; completely trustworthy.
Example
She is known for her unimpeachable honesty.
她因其无可指摘的诚实而闻名。
B1 noun /juːˈten.səlz/

Utensils

餐具
Meaning
tools or implements used for cooking, eating, or serving food
Example
Please wash all the cooking utensils after preparing dinner.
请在准备晚餐后清洗所有的厨房用具。
C1 adjective /ʌnˈsoʊld/

unsold

未售出的
Meaning
not sold; remaining without a buyer
Example
The unsold goods were returned to the warehouse.
未售出的商品被退回仓库。
C1 adjective ʌnˈmætʃt

unmatched

无与伦比
Meaning
Not equaled or rivaled by any other; without equal.
Example
The freedom fighters showed unmatched bravery.
自由战士们展示了无与伦比的勇气。
A2 verb /ʌpˈdeɪt/

update

更新
Meaning
to make something more modern or current; to provide new information
Example
Please update your software regularly.
请定期更新您的软件。
B1 adjective /ʌnˈfrɛndli/

unfriendly

不友好的
Meaning
not kind or welcoming; hostile or cold in behavior or attitude
Example
The shop owner seemed unfriendly to new customers.
店主对新顾客显得不友好。
C2 noun /juːˌtɪlɪˈtɛəriənɪzəm/

utilitarianism

功利主义
Meaning
The ethical theory that actions are right if they are useful or for the benefit of the majority.
Example
Utilitarianism suggests that we should act to maximize overall happiness.
功利主义认为我们应该采取行动，以最大化整体幸福。
C2 noun /juːˈkeɪs/

ukase

法令
Meaning
An authoritative decree or order, especially one issued by a sovereign or government.
Example
The czar issued a ukase restricting the freedom of the press.
沙皇发布了一项限制新闻自由的法令。
B2 verb /ˈjuːtɪlaɪz/

utilize

利用
Meaning
to make practical or effective use of something
Example
The company aims to utilize solar energy for production.
公司旨在利用太阳能进行生产。
B1 adjective /ʌnˈkaʊntəbəl/

Uncountable

无法计数的; 无穷的
Meaning
too many to be counted; innumerable; infinite in quantity
Example
There are uncountable stars in the night sky.
夜空中有无数的星星。
C1 adjective /ʌnˈsɪvəl/

Uncivil

不文明的; 粗鲁的;
Meaning
not polite or courteous; rude and discourteous in behavior
Example
His uncivil remarks during the meeting offended everyone present.
他在会议上的不文明言论冒犯了在场的每一个人。
B2 adverb /ʌnˈwɪlɪŋli/

unwillingly

不情愿地
Meaning
in a way that shows reluctance or lack of desire; not willingly
Example
She unwillingly agreed to attend the meeting.
她不情愿地同意参加会议。
B2 adjective /ʌnˈwɜːrði/

Unworthy

不配; 没有价值
Meaning
not deserving respect or attention; lacking worth or merit
Example
He felt unworthy of such praise and recognition.
他觉得自己不配得到这样的赞扬和认可。
C1 adjective /ˌʌnfɔːrθˈkʌmɪŋ/

unforthcoming

不合作的
Meaning
Not willing to talk or provide information; uncooperative.
Example
The witness was unforthcoming about what he had seen.
证人对于他所见的情况不合作。
B2 verb /ˌʌndərˈmaɪn/

undermine

削弱
Meaning
to gradually weaken or damage something or someone
Example
Constant criticism can undermine a child's confidence.
持续的批评可能会削弱孩子的自信心。
C2 noun /ˈʌm.brə/

Umbra

完全的阴影，太阳黑子的黑暗中心
Meaning
the fully shaded inner region of a shadow cast by an opaque object; the dark center of a sunspot
Example
During the eclipse, we stood in the moon's umbra.
在日食期间，我们站在月亮的本影中。
C2 adjective /ˌʌnrɪˈmɪtɪŋ/

unremitting

不断的
Meaning
Never relaxing or stopping; persistent.
Example
Her unremitting efforts finally paid off.
她不懈的努力终于得到了回报。
C1 adjective /ˌʌndərˈsaɪzd/

undersized

尺寸过小
Meaning
Smaller than the usual or expected size.
Example
The undersized puppy struggled to keep up with its siblings.
这只尺寸过小的小狗很难跟上它的兄弟姐妹。
B1 adjective /ʌnˈsɜːrtən/

Uncertain

不确定
Meaning
not able to be relied on; not known or definite; not having reliable knowledge
Example
I am uncertain about my future career plans.
我对未来的职业规划感到不确定。
B2 noun ˈjuːnəti

unity

团结
Meaning
The state of being united or joined as a whole.
Example
Unity among people led to victory.
人们之间的团结带来了胜利。
B2 adjective /ʌnˈiːvən/

Uneven

不平; 粗糙
Meaning
not level or smooth; not regular or consistent
Example
The road was uneven and full of potholes.
那条路不平，充满了坑洞。
C1 noun /ʌnkənˈsɜːrn/

Unconcern

漠不关心
Meaning
lack of worry or interest; indifference
Example
She showed complete unconcern about the criticism.
她对批评表现出了完全的漠不关心。
B1 adverb /ˌʌpsaɪd ˈdaʊn/

Upside-down

倒过来
Meaning
with the upper part at the bottom; in or into a reversed position
Example
The picture was hanging upside-down on the wall.
图片倒挂在墙上。
C1 adjective /ˌʌn.əˈdʌl.tə.reɪ.tɪd/

Unadulterated

纯净的
Meaning
not mixed or diluted with any different or extra elements; pure
Example
She felt unadulterated joy when she heard the news.
当她听到这个消息时，她感到纯净的快乐。
C1 adjective /ʌnˈɒnəd/

unhonoured

未受尊敬的
Meaning
not respected or given the recognition that is deserved; treated without honor
Example
He felt unhonoured after his years of service were ignored.
他的多年服务被忽视后，他感到自己未受尊敬。
B2 noun /ʌnˈrest/

Unrest

不安；动荡；社会或政治动乱
Meaning
a state of dissatisfaction and disturbance; social or political disorder
Example
The economic crisis led to widespread social unrest.
经济危机导致了广泛的社会不安。