univalence
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C2 noun /ˈjuːnɪvəˌlɛns/

univalence

单价性
Meaning
The state of having a single valence or combining power, especially in chemistry.
Example
Hydrogen is characterized by its univalence in chemical reactions.
氢气在化学反应中以其单价性为特点。
C1 adjective /ʌnˈvaɪəbl/

unviable

不可行的
Meaning
Not capable of working successfully; not feasible or practical.
Example
The project was deemed unviable due to high costs.
由于高昂的成本，该项目被认为不可行。
C1 adjective /ʌnˈdɔːntɪd/

Undaunted

无畏的; 勇敢的; 不屈的;
Meaning
not intimidated or discouraged by difficulty, danger, or disappointment
Example
Despite the setbacks, she remained undaunted in pursuing her goals.
尽管遇到挫折，她在追求目标时依然无畏。
B1 adjective /ʌnˈedjʊkeɪtɪd/

Uneducated

未受教育的; 文盲
Meaning
lacking education; not having received formal schooling or training
Example
Many uneducated workers struggle to find well-paying jobs.
许多未受教育的工人很难找到薪水高的工作。
C1 adjective /ˌʌnfɔːrˈsiːn/

unforeseen

Meaning
Not anticipated or predicted; unexpected.
Example
The project faced unforeseen challenges that delayed its completion.
C1 noun /ˈjuːnɪsən/

unison

齐声
Meaning
Simultaneous performance or utterance of action or speech.
Example
The choir sang in unison.
合唱团齐声唱歌。
C1 adjective /ˌʌndərˈhændɪd/

underhanded

阴险
Meaning
acting or done in a dishonest or secret way
Example
They exposed the company's underhanded dealings with its suppliers.
他们揭露了公司与供应商之间的隐秘交易。
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 verb /ʌnˈmɑːsk/

unmask

揭露；暴露真相
Meaning
to remove a mask or covering; to reveal the true identity, nature, or intentions of someone or something
Example
The investigation helped unmask the real culprit behind the crime.
调查帮助揭露了犯罪背后的真正罪犯。
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。
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 /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。
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 /ʌnˈsuːtəbl/

Unsuitable

不适合; 不合适
Meaning
not fitting or appropriate for a particular purpose or situation
Example
This formal dress is unsuitable for a casual beach party.
这件正式的衣服不适合参加随意的海滩派对。
A1 pronoun /ʌs/

us

我们
Meaning
used to refer to the speaker and one or more other people as the object of a verb or preposition
Example
She gave us a gift.
她给了我们一个礼物。
C2 noun /ˈjuːʒəri/

usury

高利贷
Meaning
The practice of lending money at unreasonably high interest rates.
Example
The law strictly prohibits usury.
法律严格禁止高利贷。
C1 verb /ʌnˈkɔrk/

uncork

开瓶
Meaning
To remove the cork from a bottle; to open a bottle, especially of wine
Example
He uncorked the wine and poured a glass for everyone.
他开了葡萄酒，并为每个人倒了一杯。
C1 adjective /ˌʌnəˈsjuːmɪŋ/

unassuming

谦虚
Meaning
Not pretentious or arrogant; modest.
Example
Despite his success, he remained unassuming and humble.
尽管他取得了成功，他仍然谦虚和谦逊。
B2 noun /ʌnˈsɜːrtənti/

Uncertainty

不确定性; 怀疑或缺乏确信
Meaning
the state of being uncertain; doubt or lack of sureness
Example
The uncertainty about the weather delayed our trip.
关于天气的不确定性延迟了我们的旅行。
C2 adjective /ʌnˈkɒnʃənəbl/

unconscionable

不合理的
Meaning
shockingly unfair or unreasonable
Example
The company made unconscionable profits from the crisis.
公司从危机中获得了不合理的利润。
B2 adjective /ʌnˈθɪŋkəbl/

Unthinkable

难以想象的
Meaning
impossible to conceive or imagine; beyond belief or consideration
Example
It was unthinkable that such a tragedy could happen in our peaceful town.
在我们和平的小镇上发生这样一场悲剧，简直是难以想象的。
B1 adjective /ʌnˈpɒpjʊlə/

unpopular

不受欢迎的
Meaning
not liked or supported by many people
Example
The decision was unpopular with the public.
这个决定在公众中不受欢迎。
B2 adverb /ʌnˈkaɪndli/

unkindly

残忍地
Meaning
in a cruel, harsh, or unsympathetic manner
Example
She spoke unkindly about her colleague during the meeting.
她在会议期间残忍地谈论了她的同事。
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 noun ˌɜːbənaɪˈzeɪʃən

urbanization

城市化
Meaning
The process by which towns and cities are formed and become larger as more people begin living and working in central areas.
Example
Urbanization leads to more developed infrastructure.
城市化导致更先进的基础设施。
B2 adjective /ˌʌnkənˈvɪnsɪŋ/

Unconvincing

不可信
Meaning
failing to persuade or impress; not believable or credible
Example
His excuse for being late was completely unconvincing.
他因迟到而给出的借口完全不可信。
C1 adjective /ʌnˈkwaɪ.ət/

Unquiet

不安的; 焦虑的; 激动的
Meaning
restless; unable to remain still or quiet; anxious or troubled
Example
She spent an unquiet night worrying about the exam results.
她度过了一个不安的夜晚，担心考试结果。
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。
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。
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 /ʌnˈwɪtɪŋ/

unwitting

无意的
Meaning
Not aware of what is happening; done without realizing.
Example
She became an unwitting participant in the scam.
她成了这场骗局中的一个无意的参与者。
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。
A1 verb /ˌʌndərˈstænd/

understand

理解
Meaning
to know the meaning of something; to comprehend
Example
Do you understand the instructions?
你理解这些指示吗?
C2 adjective /juːˈbɪkwɪtəs/

ubiquitious

无处不在
Meaning
Present, appearing, or found everywhere.
Example
Smartphones have become ubiquitous in modern society.
智能手机已经在现代社会中无处不在。
A1 adverb /ˈjuː.ʒu.ə.li/

Usually

通常; 一般
Meaning
in most cases; generally; as a rule
Example
I usually wake up at 7 AM every morning.
我通常每天早上7点起床。
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。
C2 noun /ʌnˈkloʊðɪŋ/

unclothing

脱衣
Meaning
the act or process of removing clothing
Example
The child quickly ran inside for unclothing after playing in the mud.
孩子在泥地玩耍后迅速跑进去脱衣。
B1 adjective /ʌnˈlaɪk/

Unlike

不同的; 不相似的
Meaning
different from; not similar to
Example
Unlike his brother, he prefers quiet activities.
与他哥哥不同，他喜欢安静的活动。
B1 adverb /ʌnˈjuːʒuəli/

unusually

异常地
Meaning
in a way that is not typical or expected; to an uncommon degree
Example
It was unusually cold for this time of year.
对一年中的这个时候来说，天气异常寒冷。
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。
C1 adjective /ʌnˈfɔːltərɪŋ/

unfaltering

坚定不移
Meaning
Steady and resolute; not weakening or hesitating
Example
She continued with unfaltering determination.
她以坚定不移的决心继续前进。
C1 adjective ʌnɪnˈhæbɪtəbəl

uninhabitable

不可居住
Meaning
Not suitable or safe for people to live in.
Example
Rapid urbanization can make cities uninhabitable.
快速城市化可能使城市变得无法居住。
A2 noun /ˈʌndərwɛr/

Under wear

内衣
Meaning
clothing worn under other clothes, next to the skin
Example
She bought new underwear from the department store.
她在百货商店买了新的内衣。
C1 adjective /ˌʌnˈɪntɪmeɪtɪŋ/

unintimating

没有暗示
Meaning
Not giving a hint or suggestion; not indicating.
Example
His unintimating tone gave no clue of his true feelings.
他的没有暗示的语气没有透露他真正的感受。
C2 verb /ʌpˈbreɪd/

upbraid

斥责
Meaning
To scold or criticize someone harshly.
Example
The teacher upbraided the student for being late again.
老师因为学生再次迟到而训斥了他。
C1 adjective /ʌnˈkuːθ/

uncouth

粗鲁
Meaning
Lacking good manners, refinement, or grace; awkward or rough.
Example
His uncouth behavior shocked the guests at the party.
他粗鲁的行为让聚会上的客人感到震惊。
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。
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。
B2 noun /ʌnˈkaɪndnəs/

unkindness

不友善
Meaning
lack of kindness; cruel or inconsiderate behavior
Example
His unkindness hurt her feelings deeply.
他的不友善深深伤害了她的感情。
B1 adjective /ʌnˈwɒn.tɪd/

Unwanted

不受欢迎的
Meaning
not desired or welcome; not wanted
Example
He felt like an unwanted guest at the meeting.
他在会议上觉得自己像个不受欢迎的客人。
C2 adjective /ʌnˈspɛərɪŋ/

unsparing

无情的
Meaning
Showing no mercy or generosity; harsh or severe.
Example
The critic was unsparing in his review of the play.
评论家在他的剧评中毫不留情。
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。
B1 adjective /ʌnˈfɔːr.tʃən.ət/

Unfortunate

不幸的；遗憾的
Meaning
having bad luck; regrettable or unlucky
Example
It was unfortunate that the meeting was cancelled at the last minute.
很不幸的是，会议在最后一刻被取消了。
C2 noun/verb /ˈʌpˌkæst/

upcast

向上投掷
Meaning
Verb: To cast or throw upward. Noun: Something thrown or directed upward.
Example
The fisherman upcast his net into the air.
渔夫把他的网投向空中。
B2 verb /ʌnˈveɪl/

unveil

揭示
Meaning
to reveal or disclose something, especially in a formal manner
Example
The company will unveil a new product next week.
公司将在下周揭示一款新产品。
C1 noun /ˈʌp.rɔːr/

Uproar

骚动; 喧嚣; 混乱
Meaning
a loud and emotional noise or disturbance; public outcry
Example
The announcement caused an uproar among the students.
公告在学生中引起了骚动。
C1 verb /ˌʌndərˈsteɪt/

understate

低估
Meaning
To describe something as being less important or serious than it really is.
Example
He tends to understate his achievements.
他倾向于低估自己的成就。
B2 adjective /ʌnˈfeɪ.vər.ə.bəl/

Unfavourable

不利的; 逆境的
Meaning
not helpful or advantageous; adverse
Example
The weather conditions were unfavourable for our outdoor event.
恶劣的天气条件不利于我们的户外活动。
B2 adverb /ʌnˈnesəserəli/

Unnecessarily

不必要地
Meaning
to a greater extent than is needed; without necessity
Example
Don't worry unnecessarily about the exam.
不要为考试不必要地担心。
B2 adjective /ˌjuːnɪˈvɜːrsəl/

Universal

普遍的
Meaning
applicable to all cases; existing everywhere
Example
Music is a universal language that everyone understands.
音乐是一种普遍的语言，人人都能理解。
B2 adjective /ʌnˈriːzənəbəl/

unreasonable

不合理的
Meaning
not guided by reason or fairness; excessive or extreme beyond what is acceptable
Example
The manager made an unreasonable demand that no one could realistically meet.
经理提出了一个不合理的要求。
C2 verb /ʌnˈfrɒk/

unfrock

剥夺神职
Meaning
To remove a priest from his position or deprive someone of a rank.
Example
The corrupt priest was unfrocked after the investigation.
腐败的牧师在调查后被解除职务。
A2 noun /ʌmˈbrɛlə/

umbrella

伞
Meaning
A device used for protection against rain or sun, typically consisting of a collapsible canopy mounted on a central rod.
Example
She opened her umbrella as it started to rain.
下雨时她打开了她的伞。
C2 noun /ˈjuːzjuːfrʌkt/

usufruct

使用权
Meaning
The legal right to use and enjoy the benefits of someone else’s property without owning it.
Example
The tenant had the usufruct of the land but not its ownership.
租户有权使用这片土地，但没有所有权。
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。
C2 adjective /ˌʌn.təˈwɔːrd/

untoward

意外的
Meaning
Unexpected and inappropriate or inconvenient.
Example
The meeting ended without any untoward incidents.
会议在没有任何意外事件的情况下结束。
C2 verb /ˌʌn.dɪˈsiːv/

undeceive

解惑
Meaning
To free someone from a misconception or false belief.
Example
She tried to undeceive him about the false rumors.
她试图让他摆脱这些错误的谣言。
B2 adjective /ˌʌnɪnˈfɔːrmd/

uninformed

不了解情况的
Meaning
lacking knowledge or awareness about a particular subject; not educated or informed
Example
The decision was made by an uninformed committee.
这个决定是由一个不了解情况的委员会做出的。
B2 adjective /ʌnprəˈdʌk.tɪv/

Unproductive

无效的; 不起作用的
Meaning
not achieving much; not producing good results
Example
The meeting was unproductive and wasted everyone's time.
会议是无效的，浪费了大家的时间。
C1 adjective /ʌlˈtɪəriər/

ulterior

隐藏的动机
Meaning
hidden or secret, often with a selfish motive
Example
He invited her with an ulterior motive.
他带着隐藏的动机邀请了她。
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。
B2 adverb /ˈɜːrdʒəntli/

urgently

紧急地
Meaning
in a way that requires immediate attention or action
Example
The patient urgently needs medical attention.
病人紧急地需要医疗救助。
B2 verb /ʌpˈhoʊld/

uphold

维护
Meaning
to maintain or support a principle, law, or decision
Example
The judge promised to uphold justice at all costs.
法官承诺不惜一切代价维护正义。
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 adjective /ˈʌl.tɪ.mət/

Ultimate

最终的; 极致的; 终极的
Meaning
being the best or most extreme example of its kind; final; last
Example
This is the ultimate test of your skills.
这是你技能的终极考验。
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 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。
B1 adjective /ˈɜːrdʒənt/

Urgent

紧急
Meaning
requiring immediate action or attention; pressing
Example
The patient needs urgent medical attention.
病人需要紧急医疗照顾。
A2 noun /ˈʌndərweər/

underwear

内衣
Meaning
Clothing worn beneath outer clothes, typically next to the skin.
Example
He bought new underwear for the trip.
他为旅行买了新的内衣。
B2 adjective /ʌnˈkɒn.ʃəs/

Unconscious

昏迷; 无意识
Meaning
not awake and aware of one's surroundings; done or existing without one realizing
Example
The patient was unconscious for several hours after the surgery.
病人在手术后昏迷了几个小时。
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。
A2 adjective /ʌnˈkʌmf.tə.bəl/

Uncomfortable

不舒服
Meaning
causing or feeling slight pain or physical discomfort; making someone feel embarrassed, awkward, or anxious
Example
The chair was so uncomfortable that I couldn't sit in it for more than ten minutes.
这个椅子太不舒服了，我坐在上面超过十分钟就坐不下来了。
B2 adjective /ʌnˌkənˈdɪʃ.ən.əl/

Unconditional

无条件的
Meaning
not subject to any conditions; complete and absolute
Example
She offered her unconditional support to her friend in need.
她在朋友需要时提供了无条件的支持。
C1 adjective /ʌnˈweɪ.vər.ɪŋ/

unwavering

坚定
Meaning
Steady or resolute; not wavering.
Example
He showed unwavering dedication to his goal.
他展示了对目标的坚定承诺。
C2 noun /ˈʌŋkʃən/

unction

涂抹
Meaning
The act of anointing as part of a religious or ceremonial ritual; excessive or insincere flattery.
Example
The priest performed the holy unction with solemnity.
牧师庄重地进行了神圣的涂抹仪式。
C2 verb /ʌnˈkaʊtʃ/

uncouch

从沙发上移开（罕见用法）
Meaning
to remove from a couch or to release from being laid down (rare/archaic usage)
Example
The surgeon attempted to uncouch the cataract.
外科医生试图去除白内障。
B2 adjective /ˌʌnˈnoʊ.tɪst/

Unnoticed

未被注意到; 被忽视
Meaning
not seen or observed; ignored
Example
His hard work went unnoticed by his manager.
他的辛勤工作没有被经理注意到。
B2 adjective /ʌnˈbreɪkəbəl/

Unbreakable

不能被打破或损坏；非常强大和耐用
Meaning
not able to be broken or damaged; very strong and durable
Example
Their friendship formed an unbreakable bond.
他们的友谊形成了一个坚不可摧的纽带。
B2 adjective /ʌnˈbæləns/

Unbalanced

不平衡的; 不稳定的
Meaning
not balanced; lacking stability or equilibrium; mentally unstable
Example
The unbalanced table kept wobbling.
不平衡的桌子摇晃着。
B1 noun /ˌʌnɪmˈplɔɪmənt/

Unemployment

失业
Meaning
the state of being unemployed; lack of paid work
Example
The unemployment rate has increased significantly this year.
今年失业率显著上升。
C2 adjective /ˌʌnsɛrəˈmoʊniəs/

unceremonious

不拘礼节/粗鲁
Meaning
Done without formality or courtesy; abrupt or rude.
Example
He made an unceremonious exit from the party.
他从派对上不拘礼节地离开。
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.
A2 adjective /ʌnˈlʌki/

Unlucky

倒霉; 不幸运
Meaning
having bad luck; unfortunate
Example
He was unlucky to miss the winning shot.
他很倒霉错过了获胜的投篮。
B2 adjective /ʌnˈɑːrmd/

unarmed

手无寸铁
Meaning
Not equipped with or carrying weapons
Example
The police found the suspect unarmed during the search.
警察在搜查过程中发现嫌疑人没有武器。
B2 adjective /ˌʌndərˈlaɪɪŋ/

underlying

基本的
Meaning
basic or hidden but important; forming the foundation of something
Example
The underlying reason for the conflict was never addressed.
冲突的根本原因从未得到解决。
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。
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。
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。
B2 adjective /ˌʌnkənˈtroʊld/

uncontrolled

无法控制的
Meaning
not restrained or managed; lacking control
Example
The wildfire spread in an uncontrolled manner, causing widespread damage.
野火以无法控制的方式蔓延，造成广泛破坏。
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 adverb /ʌnˈnætʃrəli/

unnaturally

不自然地
Meaning
in a way that is not natural or normal; excessively or strangely
Example
He smiled unnaturally, making everyone feel uncomfortable.
他不自然地笑了，让每个人都感到不舒服。
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。
C1 adjective /ʌnˈsɪvəlaɪzd/

Uncivilized

未开化的; 野蛮的;
Meaning
not developed in terms of civilization; lacking social organization and culture; barbarous
Example
The explorers encountered an uncivilized tribe deep in the Amazon rainforest.
探险者在亚马逊雨林深处遇到一个未开化的部落。
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 adjective /ˌʌnrɪˈfaɪnd/

unrefined

未精炼的
Meaning
not processed or purified; lacking polish or sophistication
Example
The unrefined oil must be processed before it can be used as fuel.
未精炼的石油在用作燃料之前必须进行加工。
C2 adjective /ʌnˈlɛtəd/

unlettered

文盲
Meaning
lacking education or the ability to read and write; illiterate
Example
The unlettered villagers relied on oral traditions to preserve their history.
那些文盲村民依赖口头传统来保存他们的历史。
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。
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 preposition, adverb, adjective /ˌʌndərˈniːθ/

underneath

在……下面
Meaning
Located directly below or beneath something
Example
The keys were hidden underneath the pile of papers.
钥匙被隐藏在那堆文件下面。
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。
B2 adjective /ˈʌt.moʊst/

Utmost

最极; 极限
Meaning
greatest; most extreme; maximum possible
Example
She showed utmost care while handling the fragile items.
她在处理脆弱物品时表现出最大的关心。
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。
C2 verb /ˌʌndərˈɡɜːrd/

undergird

支持，强化
Meaning
to provide support or foundation for; to strengthen
Example
Strong values undergird a healthy society.
强大的价值观支撑着一个健康的社会。
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。
B2 adjective /ʌnˈhɜːrt/

unhurt

毫发无损
Meaning
Not injured or harmed.
Example
She walked away from the accident unhurt.
她在事故中毫发无损。
C1 adjective /ʌnˈtʌtʃəbəl/

Untouchable

不可触碰的; 无法批评或攻击
Meaning
not able to be touched or affected; beyond criticism or attack
Example
The CEO seemed untouchable despite the scandal.
即使有丑闻，首席执行官似乎仍然是不可触碰的。
C2 adjective /ʌnˈflæpəbəl/

unflappable

冷静沉着
Meaning
calm and composed, especially in difficult situations
Example
Despite the crisis, he remained unflappable and confident.
尽管面临危机，他依然保持冷静沉着，充满自信。
B1 adjective /ˌʌnsəkˈsesfl/

Unsuccessful

失败的; 没有成功的;
Meaning
not achieving desired aims or results; failing to accomplish a purpose
Example
His unsuccessful attempt to climb the mountain left him disappointed.
他未能成功登上山顶，感到失望。
B1 verb /juˈnaɪt/

unite

联合
Meaning
to join together or combine; to bring people or things together
Example
The crisis helped unite the community.
危机帮助团结了社区。
C1 verb /ˈʌndərkʌt/

undercut

Meaning
to sell at a lower price than a competitor; to weaken or undermine something
Example
The company tried to undercut its rivals by offering lower prices.
A2 preposition /əˈpɒn/

upon

之后
Meaning
on or immediately after
Example
Upon hearing the news, he rushed to the hospital.
听到消息后，他赶到医院。