indefinitely
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C1 adverb /ɪnˈdɛfɪnətli/

indefinitely

Meaning
for an unlimited or unspecified period of time
Example
The project has been postponed indefinitely.
C1 adjective /aɪˈdɪlɪk/

idyllic

Meaning
Like an idyll; extremely happy, peaceful, or picturesque.
Example
They enjoyed an idyllic vacation by the sea.
B2 noun /ɪnˈfek.ʃən/

Infection

Meaning
the process of infecting or the state of being infected; a disease caused by germs
Example
The doctor prescribed antibiotics to treat the bacterial infection in her throat.
C1 verb /ɪnˈfleɪt/

inflate

Meaning
to fill with air or gas so it expands; to increase excessively or artificially
Example
The mechanic inflated the tire to the correct pressure.
C1 noun /ˈaɪsətəʊp/

isotope

Meaning
Atoms of the same element with equal number of protons but different numbers of neutrons.
Example
Carbon-14 is a radioactive isotope used in dating fossils.
C2 noun /ˌɪn.trəˈɡreʃ.ən/

introgression

Meaning
The transfer of genetic information from one species to another through repeated backcrossing.
Example
Introgression plays a significant role in plant breeding.
C2 adjective /ɪnˈɡlɔːriəs/

inglorious

Meaning
Causing shame or disgrace; not bringing honor or glory.
Example
The army suffered an inglorious defeat.
A2 noun /ˈɪʃ.uːz/

issues

Meaning
Important topics or problems for debate or discussion.
Example
Health issues from pollution are increasing.
C2 adjective /ɪnˈæpt/

Inapt

Meaning
not suitable; inappropriate; unfit
Example
His comment was inapt for the formal meeting.
C1 adjective /ˈɪnərmoʊst/

Innermost

Meaning
most private and secret; deepest; most personal
Example
She shared her innermost feelings with her closest friend.
C1 noun /ɪnˈɛk.wɪ.ti/

inequity

Meaning
Lack of fairness or justice; unequal distribution or treatment.
Example
Social inequity continues to be a global issue.
C1 adjective /ɪˈnɔːɡjərəl/

Inaugural

Meaning
marking the beginning of something; first; opening
Example
The president delivered his inaugural speech.
B1 verb /ɪmˈprɛs/

impress

Meaning
to cause someone to feel admiration or respect
Example
Her speech managed to impress the audience.
C2 adjective /ɪmˈpæsɪbəl/

impassible

Meaning
Incapable of suffering or feeling pain (used mainly in theological or philosophical contexts).
Example
Some philosophers argue that God is impassible and cannot experience human emotions.
C1 noun /ɪmˈpjʊərəti/

impurity

Meaning
the state of being unclean or contaminated; a substance that makes something impure
Example
The scientist removed every impurity from the water sample.
C1 noun ˌɪn.fɪlˈtreɪ.ʃən

infiltration

Meaning
The process of entering or gaining access to an organization or place surreptitiously.
Example
Cybersecurity prevents infiltration into sensitive data.
A2 verb /ɪnˈkluːd/

include

Meaning
to have as part of a whole; to contain or comprise
Example
The price includes all taxes.
B2 adjective /ɪˈrɪˌspɑn.sə.bəl/

Irresponsible

Meaning
lacking a sense of responsibility; careless
Example
It was irresponsible of him to leave without telling anyone.
C2 adjective /ɪˈmɪsəbl/

immiscible

Meaning
Describes liquids that do not mix together.
Example
Oil and water are immiscible liquids.
B1 adjective /ˌɪmpəˈlaɪt/

impolite

Meaning
Not showing good manners; rude.
Example
It is impolite to interrupt someone while they are speaking.
C1 adjective /ɪˈrɛfjʊtəbəl/

Irrefutable

Meaning
impossible to deny or disprove; undeniable
Example
The evidence against him was irrefutable.
C2 adjective /ˌɪnkoʊˈɜːrsəbl̩/

incoercible

Meaning
Not capable of being forced, compelled, or restrained.
Example
Her incoercible spirit inspired others to fight for justice.
C1 adjective /ɪnˈdʒʊəriəs/

injurious

Meaning
Causing or likely to cause harm or damage.
Example
Smoking is injurious to health.
B2 noun /ɪnˈdʌstriəl ˌrɛvəˈluːʃən/

Industrial Revolution

Meaning
The rapid development of industry that occurred in Britain in the late 18th and 19th centuries, brought about by the introduction of machinery and characterized by the use of steam power and the growth of factories.
Example
The Industrial Revolution marked a shift in production processes.
B2 noun ˈɪn.frəˌstrʌk.tʃər

infrastructure

Meaning
The basic physical and organizational structures and facilities needed for the operation of a society or enterprise.
Example
Digital infrastructure is vital for future advancements.
C2 noun /ˌɪkθiˈɒlədʒi/

ichthyology

Meaning
The branch of zoology that deals with fish.
Example
He pursued a degree in ichthyology at the university.
C1 verb /ɪnˈstɪl/

instill

Meaning
to gradually but firmly establish an idea, attitude, or habit in someone's mind
Example
Parents try to instill good values in their children.
A1 preposition /ˈɪntuː/

into

Meaning
expressing movement or direction to the inside of something
Example
She walked into the room quietly.
C1 noun /ɪnˈdjuːsmənt/

inducement

Meaning
something that persuades or encourages someone to do something
Example
The company offered a bonus as an inducement to employees.
C1 adjective /ɪmˈprɒbəbl/

improbable

Meaning
Not likely to be true or to happen.
Example
It seems improbable that he will arrive on time.
C1 adverb /ɪnˈvɜːrs.li/

Inversely

Meaning
in a way that is opposite or contrary; in reverse order or manner
Example
The price of goods is inversely related to their availability in the market.
C2 noun /ɪmˈpjuːɪsəns/

impuissance

Meaning
inability to take effective action; helplessness
Example
The government’s impuissance in the face of crisis frustrated the people.
C2 noun /ˈɪrɪɡənt/

irrigant

Meaning
A liquid used for irrigation, especially in medical or agricultural contexts.
Example
The doctor used a sterile irrigant during the procedure.
C1 noun ɪnˈsɒl.vən.si

insolvency

Meaning
The state of being unable to pay debts owed; bankruptcy.
Example
The company declared insolvency after years of losses.
C1 adjective /ˌɪnɑːrˈtɪkjʊlət/

inarticulate

Meaning
Unable to express oneself clearly or effectively in speech or writing.
Example
She became inarticulate with emotion during the speech.
B1 adjective ˈɪnəveɪtɪv

innovative

Meaning
Featuring new methods; advanced and original
Example
Innovative strategies are required to combat pollution.
C1 verb /ɪnˈtɒksɪkeɪt/

intoxicate

Meaning
to make someone lose control of their faculties or behavior due to alcohol or drugs
Example
The strong drink quickly intoxicated him.
B1 noun /ɪmˈprɛʃən/

impression

Meaning
an idea, feeling, or opinion about something or someone
Example
The book gave me a good first impression.
C1 adjective /ˈɪmpjəd(ə)nt/

impudent

Meaning
not showing due respect for another person; rude
Example
The impudent child talked back to the teacher.
C2 adjective /ˌɪndɪˈtɜːrmənət/

indeterminate

Meaning
Not exactly known, defined, or established; vague or uncertain.
Example
The project was delayed for an indeterminate amount of time.
B1 adjective /ˈɪnəsənt/

Innocent

Meaning
free from guilt or sin; pure; harmless; naive
Example
The innocent child had no idea that her parents were planning a surprise party.
C2 adjective ɪnˈdɒm.ɪ.tə.bəl

indomitable

Meaning
Impossible to subdue or defeat.
Example
Her indomitable spirit helped her overcome adversity.
C2 noun /ˌɪmprɪˈkeɪʃən/

imprecation

Meaning
A spoken curse or expression of strong condemnation.
Example
The angry crowd hurled imprecations at the corrupt official.
C2 noun /ˈɪd.i.ə.si/

Idiocy

Meaning
extremely stupid behavior or actions; foolishness
Example
The decision to ignore safety protocols was pure idiocy that endangered everyone.
B1 noun /ɪnˈvɛstər/

investor

Meaning
a person or organization that puts money into financial schemes, property, or business ventures with the expectation of achieving a profit
Example
The investor funded the startup with a large sum of money.
C2 adjective /ɪnˈvɛtərət/

inveterate

Meaning
having a long-established habit, activity, or interest that is unlikely to change
Example
He is an inveterate reader who spends hours in the library every day.
B2 noun /ˈaɪkɒn/

icon

Meaning
A person or thing regarded as a symbol of something, or a graphic symbol on a screen.
Example
The singer became a cultural icon.
C1 verb /ɪnˈklaɪn/

incline

Meaning
to feel willing or favorably disposed toward something; to bend or tilt
Example
She is inclined to agree with the proposal.
C2 verb /ɪnˈsteɪt/

instate

Meaning
To set up in position, office, or authority.
Example
The board decided to instate her as the new director.
B2 noun /ɪnˈsɪstəns/

insistence

Meaning
the act of demanding something firmly or repeatedly
Example
At his insistence, we stayed longer.
B2 adjective /ˌɪnsɪɡˈnɪfɪkənt/

insignificant

Meaning
Too small or unimportant to be worth considering.
Example
The cost was so insignificant that nobody noticed it.
C1 adjective /ˌɪnsɪˈdɛntəl/

incidental

Meaning
happening as a minor part or in connection with something else
Example
Incidental expenses like snacks and tips were included in the bill.
C1 noun /ˌɪntərˈmɪʃən/

intermission

Meaning
A pause or break, especially during a performance or event.
Example
The play had a twenty-minute intermission.
B1 noun /ɪmˈpruːvmənt/

improvement

Meaning
the act of making something better
Example
There has been a significant improvement in his health.
C1 noun /ˌɪntərˈdʒɛkʃən/

interjection

Meaning
a word or phrase used to express sudden emotion or reaction, often standing alone
Example
Words like 'wow' and 'ouch' are common interjections in English.
C1 verb /ɪˈmɔːrtəlaɪz/

immortalize

Meaning
to preserve the memory of someone or something forever
Example
The statue was built to immortalize the hero’s sacrifice.
C2 adjective /ɪnˈɡreɪʃiˌeɪtɪŋ/

ingratiating

Meaning
Charming or flattering in a way intended to gain favor.
Example
His ingratiating smile made everyone trust him quickly.
C1 adjective ˌɪn.təˈstel.ər

interstellar

Meaning
Occurring or situated between stars.
Example
Scientists study interstellar travel possibilities.
B1 noun ɪnˈvestmənt

investment

Meaning
The action or process of investing money for profit or material result.
Example
Investment in waste management infrastructure is essential.
C2 adjective /ˌɪnkɒntrəˈvɜːtəbl/

incontrovertible

Meaning
impossible to deny or dispute; unquestionable
Example
The evidence was incontrovertible and proved his innocence.
C1 verb /ɪnˈtɪmɪdeɪt/

intimidate

Meaning
To frighten or overawe someone, especially to make them do what one wants.
Example
The bully tried to intimidate the smaller kids.
C1 noun /ɪnˈdaɪtmənt/

indictment

Meaning
a formal charge or accusation of a serious crime
Example
The indictment accused the company of multiple violations.
C2 adjective /ɪnˈkɒŋɡruənt/

incongruent

Meaning
Not in harmony or keeping with the surroundings or other aspects.
Example
His casual outfit looked incongruent at the formal dinner.
C1 noun /ˌɪntəkəˈnɛktɪvɪti/

interconnectivity

Meaning
The state of being interconnected or the degree of connectivity between components
Example
The rise of interconnectivity has transformed global communication.
B1 noun ˌɪndɪˈpendəns

independence

Meaning
The fact or state of being independent; freedom from outside control; not being subject to another's authority.
Example
Independence inspired the movement.
C1 noun /ɪnˈvɜːrʒən/

inversion

Meaning
A reversal of the normal order, position, or relationship.
Example
In poetry, inversion is often used to create emphasis.
C1 adjective /ɪˈnuːmərəbəl/

Innumerable

Meaning
too many to be counted; countless; infinite in number
Example
There are innumerable stars in the night sky that we cannot see with our naked eyes.
C2 noun /ɪnˈtɒksɪkənt/

intoxicant

Meaning
a substance, especially alcohol or a drug, that causes intoxication
Example
Alcohol is the most commonly used intoxicant in many cultures.
C1 adjective /ɪnˈtændʒəbl/

intangible

Meaning
Unable to be touched or grasped; not having a physical presence.
Example
Trust is an intangible quality in relationships.
C1 adjective /ˌɪrɪˈvɜːrsəbl/

irreversible

Meaning
Not able to be undone, changed, or reversed.
Example
The damage caused by the fire was irreversible.
B1 adjective /ɪˈmiːdiət/

immediate

Meaning
happening or done without delay
Example
The doctor gave her immediate attention.
C2 adjective /ɪnˈɛstɪməbl/

inestimable

Meaning
Too great or valuable to be measured or estimated.
Example
Her contribution to the project was of inestimable value.
B2 noun ˌɪr.ɪˈɡeɪ.ʃən

irrigation

Meaning
The artificial application of water to land or soil.
Example
Irrigation systems improve crop yields in dry regions.
B2 adjective /ɪmˈpɪəriəl/

imperial

Meaning
Relating to an empire or emperor; having supreme authority.
Example
The imperial palace was a symbol of the emperor's power.
C1 adjective, noun /ɪnˈdɪkətɪv/

indicative

Meaning
Serving as a sign or expression of something; in grammar, a mood used to make factual statements.
Example
His tone was indicative of his frustration.
C1 adjective /ɪnˈveɪsɪv/

invasive

Meaning
Tending to spread harmfully, intruding aggressively, or encroaching beyond proper boundaries.
Example
The doctor explained that the procedure was minimally invasive.
C2 adjective /ɪnˈsɪpɪd/

insipid

Meaning
lacking flavor, interest, or excitement; dull
Example
The soup was insipid and needed more seasoning.
C2 adjective /ɪˈnɪm.ɪ.tə.bəl/

inimitable

Meaning
So good or unusual as to be impossible to copy; unique.
Example
His inimitable writing style made him a literary legend.
C2 noun /ˈɪn.tɪ.ɡreɪ.tɪv dɪˈpləʊ.mə.si/

integrative diplomacy

Meaning
A diplomatic approach that seeks to combine or coordinate different elements, interests, or parties into a unified whole.
Example
Integrative diplomacy strengthens alliances.
C2 noun /ɪmˈbroʊlioʊ/

imbroglio

Meaning
An extremely confused, complicated, or embarrassing situation.
Example
The political imbroglio lasted for months without resolution.
C2 adjective /ɪmˈprɒvɪdənt/

improvident

Meaning
Not having or showing foresight; spending wastefully or without thought for the future.
Example
His improvident habits left him with no savings.
C1 adjective /ɪmˈpɜːrviəs/

impervious

Meaning
Not allowing fluid to pass through; unable to be affected by something.
Example
The jacket is impervious to rain.
C1 verb /ˌɪn.tɚˈtwaɪn/

intertwine

Meaning
To connect or link closely; to twist together or combine closely.
Example
Their lives became intertwined through years of friendship.
C2 noun /ɪmˌprɒb.əˈbɪl.ə.ti/

Improbability

Meaning
the quality or state of being improbable; unlikely to be true or to happen
Example
The improbability of winning the lottery twice didn't stop her from buying tickets.
C2 noun /ɪnˈsɪpiəns/

incipience

Meaning
the beginning or initial stage of something
Example
The project was still in its incipience when funding was approved.
C2 noun /ɪnˌtɛl.ɪˈdʒɛntsi.ə/

intelligentsia

Meaning
The group of people engaged in intellectual and cultural pursuits in a society.
Example
The intelligentsia played a key role in shaping public opinion.
C2 adjective /ɪnˈsɛptɪv/

inceptive

Meaning
Relating to or marking the beginning or initial stage of something.
Example
The inceptive phase of the project was marked by enthusiastic planning.
C2 adjective /ˌaɪsəʊˈθɜːrməl/

isothermal

Meaning
Having or maintaining equal or constant temperature.
Example
The experiment was conducted under isothermal conditions.
C1 adjective /ˌɪntərˈtwaɪnd/

intertwined

Meaning
closely connected or twisted together
Example
Their lives became deeply intertwined after the accident.
C2 adjective /ɪnˈvɪdiəs/

invidious

Meaning
likely to arouse resentment, envy, or anger in others
Example
The manager's invidious remarks created tension among the employees.
C2 noun /ˈɪn.dɪ.dʒəns/

indigence

Meaning
a state of extreme poverty or destitution
Example
The charity was founded to help people living in indigence.
C2 verb /ɪnˈdʒɛst/

ingest

Meaning
To take food, drink, or another substance into the body, usually by swallowing.
Example
The patient must ingest the medicine with water.
B2 adjective ˈɪn.tɪ.ɡrəl

integral

Meaning
Necessary to make a complete whole; essential or fundamental.
Example
Exercise is an integral part of a healthy lifestyle.
C1 verb /ɪnˈvoʊk/

invoke

Meaning
to call upon a higher power, authority, or principle for help, support, or justification
Example
The lawyer invoked the constitution to defend his client.
C2 noun (compound/erroneous entry) /ɪnˈɛksərəbl ɑːrmi/

inexorableinexorablearmy

Meaning
This appears to be a corrupted or concatenated form; interpreted as 'inexorable army' — an unstoppable or relentless force.
Example
The rebels feared the inexorable army approaching their stronghold.
C2 noun /ˈɪsməs/ or /ˈɪsθməs/

isthmus

Meaning
A narrow strip of land connecting two larger land areas, often with water on either side.
Example
The Panama Canal cuts through the Isthmus of Panama.
C2 adjective /ˌɪrɪˈlɪdʒəs/

irreligious

Meaning
Indifferent or hostile to religion
Example
Some people in the community consider him irreligious because he never attends religious services.
B1 adjective /ɪˈnɪʃəl/

initial

Meaning
Existing or occurring at the beginning.
Example
Her initial reaction was one of surprise.
C2 noun /ˌɪndɛnˈteɪʃən/

indentation

Meaning
A space left at the beginning of a line of text; a notch or deep recess on a surface.
Example
The teacher asked the students to use proper indentation in their essays.
C1 adjective /ɪnˈɛlɪdʒəbəl/

Ineligible

Meaning
not qualified or entitled to participate or be chosen; unsuitable
Example
Students with poor grades are ineligible for the scholarship program.
C1 adjective ˌɪn.tə.dʒen.əˈreɪ.ʃən.əl

intergenerational

Meaning
Existing or occurring between different generations of a family.
Example
Intergenerational wisdom ensures cultural continuity.
C2 adjective /ɪnˈkɒnstənt/

inconstant

Meaning
frequently changing; not consistent or dependable
Example
His inconstant moods made it difficult to work with him.
C1 noun /ɪnˈtruː.ʒən/

intrusion

Meaning
Unauthorized entry into a system or place without permission
Example
The company detected an intrusion in its server.
A2 verb /ɪnˈvaɪtɪd/

invited

Meaning
asked someone formally or politely to go somewhere or do something
Example
She was invited to the party.
C1 adjective /ɪˈrɛvərənt/

irreverent

Meaning
showing a lack of respect for people or things that are usually respected
Example
The comedian’s irreverent jokes offended some of the audience.
C2 noun /ˌɪnkænˈdɛsəns/

incandescence

Meaning
the emission of light from a hot object; brilliance
Example
The incandescence of the candle filled the dark room.
C1 adjective /ɪnˈfɜːm/

infirm

Meaning
Weak, especially due to old age or illness.
Example
The infirm old man needed assistance to walk.
B2 adjective /ˈɪnfɪnɪt/

infinite

Meaning
limitless or endless in space, extent, or number
Example
The universe is often described as infinite.
C2 adjective /ˈɪnmoʊst/

inmost

Meaning
Situated at the very heart or deepest part; most private or secret.
Example
She revealed her inmost thoughts to her closest friend.
C1 adjective /ˈɪnsələnt/

insolent

Meaning
showing a rude and arrogant lack of respect
Example
The insolent student refused to follow the teacher's instructions.
C1 adjective /ɪnˈvɛntɪv/

inventive

Meaning
Having the ability to create or design new things or to think originally.
Example
The inventor was known for his inventive solutions to everyday problems.
C2 noun /ˈɪrɪtənsi/

irritancy

Meaning
the quality or state of causing irritation; legal or formal invalidation
Example
The constant noise became an irritancy to the neighbors.
C1 verb /ɪnˈtruːd/

intrude

Meaning
To enter a place or situation where one is not wanted or not invited.
Example
He felt embarrassed to intrude on their private conversation.
C2 noun /ɪnˈsuːsiəns/

insouciance

Meaning
Casual lack of concern; indifference.
Example
She carried herself with an air of insouciance, unbothered by the challenges ahead.
B2 adjective /ˌɪnkənˈviːniənt/

Inconvenient

Meaning
causing trouble, difficulties, or discomfort; awkward; troublesome
Example
The broken elevator made it inconvenient to reach the top floor.
C2 adjective /ɪnhɑːrˈmoʊniəs/

Inharmonious

Meaning
lacking harmony; discordant in sound; not in tune
Example
The inharmonious sounds from the broken piano made everyone cover their ears.
C1 adjective /ɪˈlɪsɪt/

illicit

Meaning
Forbidden by law, rules, or custom.
Example
The police shut down the illicit drug operation.
C2 adjective /ˌɪnsəˈprɛsəbl/

insuppressible

Meaning
That cannot be suppressed or restrained.
Example
She had an insuppressible urge to laugh during the ceremony.
C2 adjective /ˌɪnkənˈsɪdərəbl/

inconsiderable

Meaning
Too small or unimportant to be worth considering.
Example
The donation was not inconsiderable, though smaller than expected.
C2 verb /ɪmˈpjuːt/

impute

Meaning
to attribute a fault or responsibility to someone
Example
They imputed the company's success to good leadership.
C1 noun /aɪl/

isle

Meaning
A small island or peninsula, often poetic or literary.
Example
They spent their honeymoon on a beautiful tropical isle.