invaluable
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C1 adjective /ɪnˈvæljʊəbl/

invaluable

Meaning
Extremely useful or indispensable.
Example
Her advice proved invaluable to my success.
C1 adjective /ɪnˈveə.ri.ə.bəl/

Invariable

Meaning
never changing; constant; always the same
Example
His invariable routine includes morning exercise and coffee.
C2 noun /ɪˌledʒ.əˈbɪl.ə.ti/

Illegibility

Meaning
the quality of being impossible or difficult to read; unclear writing or print
Example
The doctor's handwriting was famous for its illegibility among the pharmacy staff.
C2 adjective /ˌɪnkəmˈbʌstəbl/

incombustible

Meaning
Not capable of catching fire or burning.
Example
This material is incombustible and safe for construction.
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.
C1 adjective ɪnˈtrɪn.zɪk

intrinsic

Meaning
Belonging naturally; essential. Existing as a natural or basic part of something.
Example
Creativity is an intrinsic quality of a great artist.
B2 verb /ɪnˈfɜːr/

infer

Meaning
to conclude or deduce something from evidence and reasoning rather than from explicit statements
Example
From his silence, I inferred that he was not happy with the decision.
C1 adjective ɪmˈpɛkəbl

impeccable

Meaning
In accordance with the highest standards; faultless.
Example
His impeccable taste in fashion was admired by all his peers.
C1 adjective /ɪnˈflæməbəl/

Inflammable

Meaning
easily set on fire; flammable; combustible
Example
The inflammable material caught fire quickly.
C1 noun /ˈɪntrɪkəsi/

intricacy

Meaning
the quality of being very detailed or complicated
Example
The intricacy of the design impressed everyone.
C1 noun ˌɪn.toʊˈneɪ.ʃən

intonation

Meaning
The rise and fall of tone in speech and pronunciation.
Example
Proper intonation enhances the clarity of a speech.
C2 noun /ɪmˈpruː.dəns/

Imprudence

Meaning
the quality of being imprudent; lack of care for consequences; recklessness
Example
His financial imprudence led to bankruptcy within just two years.
C1 noun /ˈɪntərˌpleɪ/

interplay

Meaning
The way in which two or more things have an effect on each other.
Example
The interplay between culture and technology shapes modern life.
C1 noun /ˌɪndɪˈdʒɛstʃən/

indigestion

Meaning
Discomfort or pain in the stomach associated with difficulty in digesting food.
Example
He avoided spicy food because it often gave him indigestion.
C1 noun /aɪˈdiː.ə.lɪ.zəm/

Idealism

Meaning
the pursuit of high principles and noble goals; unrealistic pursuit of perfection
Example
His youthful idealism motivated him to join various social justice movements.
C2 noun /ˌɪrɪˈdɛsəns/

iridescence

Meaning
a play of lustrous, changing colors like those of a rainbow
Example
The butterfly's wings shimmered with iridescence.
C2 noun /ˌɪmprɪˈkeɪʃən/

imprecation

Meaning
A spoken curse or expression of strong condemnation.
Example
The angry crowd hurled imprecations at the corrupt official.
B2 noun /ɪnˈspekʃən/

inspection

Meaning
a careful examination of something, especially to check that it is correct or safe
Example
The building passed the safety inspection last week.
C1 verb /ɪnˈkɑːrsəreɪt/

incarcerate

Meaning
to imprison or confine someone
Example
The authorities incarcerated the criminal after the trial.
B2 noun ˈɪnər strɛŋkθ

inner strength

Meaning
Mental or spiritual power that helps a person cope with difficulties.
Example
Community service fosters inner strength in individuals.
C2 noun /ˈaɪdlər/

idler

Meaning
A person who avoids work or spends time lazily.
Example
He was known as an idler who wasted his days.
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.
A2 noun/adjective /ˌɪndɪˈvɪdʒuəl/

individual

Meaning
A single human being as distinct from a group; relating to one person.
Example
Each individual has the right to freedom of speech.
C2 noun /ɪnˈvaɪtər/

invitor

Meaning
a person who invites someone to an event, meeting, or place
Example
The invitor greeted all the guests warmly at the entrance.
B2 verb /ɪmˈplaɪ/

imply

Meaning
To suggest something without directly stating it.
Example
Her tone seemed to imply that she was upset.
C1 adjective ɪnˈdʒiː.ni.əs

ingenious

Meaning
Showing inventiveness and skill; clever, original, and inventive.
Example
His ingenious ideas transformed modern physics.
C2 noun /ˌɪnəməˈrɑːtə/

inamorata

Meaning
A woman with whom someone is in love; a female lover.
Example
He wrote a poem dedicated to his inamorata.
C1 verb /ˈɪnfɪltreɪt/

infiltrate

Meaning
to secretly enter or gain access to a place or group
Example
The spies managed to infiltrate the enemy base.
C2 noun /ɪnˈkwɪzɪtər/

inquisitor

Meaning
A person who asks many questions, often in an official or harsh manner.
Example
The inquisitor demanded detailed answers from the witness.
C2 noun /ˈɪndələns/

indolence

Meaning
Avoidance of activity or exertion; laziness.
Example
His indolence kept him from finishing the project on time.
C1 adjective /ɪmˈpɛn.ɪ.trə.bəl/

impenetrable

Meaning
Impossible to pass through or enter; impossible to understand.
Example
The dense forest was nearly impenetrable.
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.
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.
C2 noun /ˌɪnˌkeɪpəˈbɪləti/

incapability

Meaning
lack of ability or power to do something; inability or incompetence
Example
His incapability to manage the team led to serious problems.
C2 verb /ɪnˈsɪnəˌreɪt/

incinerate

Meaning
to burn something completely until it is reduced to ashes
Example
The city decided to incinerate the medical waste for safety.
C1 verb ɪˈmɜːrs

immerse

Meaning
To involve oneself deeply in a particular activity or interest; to surround completely.
Example
Immerse yourself in the new language.
C1 adjective /ɪˈmuː.və.bəl/

immovable

Meaning
Not able to be moved; fixed in position.
Example
Immovable barriers prevent change.
C1 verb /ɪnˈsɪnjueɪt/

insinuate

Meaning
To suggest or hint something indirectly and often unpleasantly.
Example
He insinuated that she had lied about her qualifications.
C1 adjective ɪˈluː.sər.i

illusory

Meaning
Based on illusion; not real although seeming to be.
Example
His sense of security was entirely illusory.
A1 preposition /ɪn/

in

Meaning
expressing the situation of being enclosed or surrounded by something
Example
She is in the kitchen preparing dinner.
C1 adjective /ˌɪnəˈfɛnsɪv/

inoffensive

Meaning
Not likely to offend or provoke; harmless.
Example
His inoffensive remarks kept the conversation friendly.
C1 verb /ɪnˈfleɪm/

inflame

Meaning
to arouse strong feelings or provoke anger; to cause inflammation in the body
Example
The politician's remarks served to inflame public opinion.
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.
C2 verb /ɪnˈfætʃueɪt/

infatuate

Meaning
to inspire with an intense but short-lived passion or admiration
Example
He was infatuated with her beauty.
B2 adjective /ɪnˈvɪz.ə.bəl/

Invisible

Meaning
unable to be seen; not visible to the eye
Example
The bacteria are invisible without a microscope.
B2 adjective /ɪmˈplɪsɪt/

implicit

Meaning
Suggested or understood without being directly stated.
Example
Her trust in him was implicit.
B1 verb /aɪˈdentɪfaɪ/

identify

Meaning
to recognize; to establish who someone is
Example
Can you identify the suspect?
C1 noun /ˈɪtʃ.i.nəs/

itchiness

Meaning
The quality or condition of feeling an irritating sensation on the skin that causes a desire to scratch.
Example
Eye itchiness often leads to rubbing.
B1 noun /ˈɪnstrəmənt/

instrument

Meaning
A tool or device used for a particular purpose, especially for scientific or musical work.
Example
The doctor used a special instrument during the surgery.
C2 adjective /ɪnˈkɒntɪnənt/

incontinent

Meaning
lacking control over urination or defecation; lacking self-restraint
Example
The patient was incontinent after surgery.
B1 verb /ɪnˈstɔːl/

install

Meaning
To place or fix equipment or software so it is ready for use.
Example
He installed the new software on his computer.
C2 adjective /ɪnˈvaɪələbl/

inviolable

Meaning
never to be broken, dishonored, or violated
Example
Human rights are considered inviolable in modern democracies.
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 adjective /ɪnˈeɪliənəbl/

inalienable

Meaning
Unable to be taken away or transferred; absolute and permanent.
Example
Freedom of speech is an inalienable right.
B2 noun ˈɪndɪkeɪtə

indicator

Meaning
A thing that indicates the state or level of something.
Example
The unemployment rate is a key indicator of economic health.
C2 verb /ˈɪndjʊˌreɪt/

indurate

Meaning
To harden or make something physically or emotionally tough.
Example
Years of hardship indurated his spirit.
B2 adjective /ˌɪnkənˈsɪstənt/

inconsistent

Meaning
Not staying the same throughout; lacking harmony or regularity.
Example
His answers were inconsistent and confusing.
C1 noun /ɪnˈtruː.ʒən/

intrusion

Meaning
Unauthorized entry into a system or place without permission
Example
The company detected an intrusion in its server.
C1 adjective /ɪnˈtɒl.ər.ə.bəl/

Intolerable

Meaning
unable to be endured; extremely unpleasant or painful
Example
The noise from the construction site was intolerable.
C1 verb /ɪmˈpɛər/

impair

Meaning
to weaken or damage something, especially a function or ability
Example
Smoking can impair your lung capacity.
C1 noun /ɪnˈfɜː.mə.ti/

Infirmity

Meaning
physical or mental weakness; a disease or ailment; frailty
Example
Despite his advanced age and various infirmities, he remained mentally sharp and alert.
C2 noun /ɪnˈtɜːrstɪs/

interstice

Meaning
a small space that lies between things
Example
Light filtered through the narrow interstices of the wall.
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.
C1 adjective /ɪnˈɔːdəbl/

inaudible

Meaning
Unable to be heard.
Example
Her voice was almost inaudible over the noise.
C2 adjective /ɪnˈvʌlnərəbl/

invulnerable

Meaning
Impossible to harm, damage, or defeat.
Example
The fortress was thought to be invulnerable to attack.
B2 adjective /ɪˈrɪˌspɑn.sə.bəl/

Irresponsible

Meaning
lacking a sense of responsibility; careless
Example
It was irresponsible of him to leave without telling anyone.
C1 verb /ɪnˈfɛst/

infest

Meaning
to overrun in large numbers, especially so as to cause damage or discomfort
Example
The old house was infested with rats.
C2 adjective /ɪmˌpɜːrˈsweɪdəbl/

impersuadable

Meaning
not able to be convinced or persuaded
Example
She remained impersuadable despite all our arguments.
B2 adjective /ɪnˈækjərət/

Inaccurate

Meaning
not correct; containing errors; wrong
Example
The weather forecast was inaccurate yesterday.
C1 verb /ɪmˈpɜːrsəneɪt/

impersonate

Meaning
to pretend to be another person in order to entertain or deceive
Example
He was arrested for trying to impersonate a police officer.
B2 adjective /ɪnˈstrʌkʃənəl/

instructional

Meaning
providing knowledge or information; intended to teach
Example
The website offers many instructional videos for beginners.
B2 noun ɪnˈfleɪʃən

inflation

Meaning
A general increase in prices and fall in the purchasing value of money.
Example
Inflation erodes the purchasing power of consumers.
A2 adjective /ɪl/

Ill

Meaning
sick; unwell; in poor health
Example
He felt ill and decided to stay home from work.
B2 verb /ɪnˈtɜːrprət/

interpret

Meaning
to explain the meaning of something; to translate orally
Example
She had to interpret the speech for the foreign guests.
C2 noun /ˌɪntərˈsɛʃən/

intercession

Meaning
the act of intervening or pleading on behalf of another person
Example
The prisoner was released due to the intercession of influential leaders.
C2 verb /ˌɪntərˈpoʊz/

interpose

Meaning
To place or insert between one thing and another; to intervene in a situation.
Example
He quickly interposed himself between the fighters to stop the quarrel.
C2 noun /ˈɪɡ.nəˌmɪn.i/

ignominy

Meaning
Public shame, disgrace, or dishonor.
Example
He lived the rest of his life in ignominy after the scandal.
C1 noun /ˈɪŋklɪŋ/

inkling

Meaning
A slight idea, hint, or suspicion about something.
Example
She had an inkling that he was planning a surprise.
C2 verb /ɪmˈpjuːt/

impute

Meaning
to attribute a fault or responsibility to someone
Example
They imputed the company's success to good leadership.
C2 adjective /aɪˈtɪnərənt/

itinerant

Meaning
Traveling from place to place, especially for work or duty.
Example
The itinerant teacher moved from village to village to educate children.
C2 adjective /ˌɪrɪˈdɛsənt/

iridescent

Meaning
showing luminous colors that seem to change when seen from different angles
Example
She wore an iridescent dress that sparkled in the light.
C1 noun /ɪnˈfɜːməri/

infirmary

Meaning
A hospital or place where the sick or injured are cared for.
Example
The school had an infirmary for minor injuries.
B2 adjective /ˌɪn.trəˈdʌk.tər.i/

introductory

Meaning
Serving as an introduction; preliminary or preparatory.
Example
The professor gave an introductory lecture on economics.
C1 adjective /ˌɪnɪkˈskjuːzəbl/

inexcusable

Meaning
Too bad to be justified or overlooked; unforgivable.
Example
His rude behavior was inexcusable.
B1 verb ɪnˈspaɪər

inspire

Meaning
To fill someone with the urge or ability to do or feel something, especially creative or noble.
Example
Artemis seeks to inspire future generations.
B2 noun /ɪnˈtɒlərəns/

intolerance

Meaning
unwillingness to accept or endure beliefs, behaviors, or conditions different from one's own
Example
The leader was criticized for his intolerance toward other religions.
C1 verb /ˌɪn.trəˈspekt/

introspect

Meaning
To examine one's own thoughts, feelings, or mental state.
Example
He often introspects before making important decisions.
C1 verb /ˈɪnsjuleɪt/

insulate

Meaning
To protect something by covering it, especially to prevent heat, sound, or electricity from escaping or entering.
Example
The house was insulated to reduce heating costs.
B2 adjective /ɪˈmædʒɪnəbl/

imaginable

Meaning
Capable of being imagined or conceived.
Example
They offered every imaginable type of food at the festival.
C1 adjective ˈɪn.lənd

Inland

Meaning
Situated in the interior of a country; away from the coast.
Example
Inland transport boosts local trade.
C1 adverb /ˌɪn.dɪˈskrɪm.ɪ.nət.li/

Indiscriminately

Meaning
without making careful distinctions; randomly; without discrimination
Example
The company fired employees indiscriminately without considering their performance.
C1 adverb, adjective /ˌɪnkɑːɡˈniːtoʊ/

incognito

Meaning
In disguise or with one's identity concealed.
Example
The celebrity traveled incognito to avoid the paparazzi.
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 adjective /ˌɪlˈneɪ.tʃəd/

ill-natured

Meaning
Having a bad or unpleasant character; unkind or malicious.
Example
He made an ill-natured remark about his colleague.
C2 verb /ɪmˈpjuːn/

impugn

Meaning
to dispute the truth, validity, or honesty of a statement or motive
Example
The lawyer tried to impugn the credibility of the witness.
C2 noun /ˌɪnvəˈlɪdɪti/

invalidity

Meaning
the state of being invalid, legally void, or lacking force or validity
Example
The court ruled that the contract suffered from invalidity.
C2 noun /ɪmˌpɜːrtərbəˈbɪləti/

imperturbability

Meaning
The quality of being calm and not easily disturbed or upset.
Example
Her imperturbability during the crisis impressed everyone.
B2 noun /ɪnˈtɛnsəti/

intensity

Meaning
The quality of being extreme, strong, or forceful in degree.
Example
The intensity of the storm frightened the villagers.
C2 adjective /ˈɪkθiɪk/

ichthyic

Meaning
Relating to or resembling fish.
Example
The artist's painting had an ichthyic quality.
B1 noun /ˌɪntərˈækʃən/

interaction

Meaning
The process of people or things acting upon or influencing each other.
Example
The teacher encouraged more interaction between students.
B2 noun /ɪnˈkluːʒən/

inclusion

Meaning
the action or state of including or being included within a group or structure
Example
Diversity and inclusion are key values in modern workplaces.
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.
B2 adjective /ˌɪntərˈmiːdiət/

intermediate

Meaning
Coming between two things in time, place, or order; in the middle level or stage.
Example
She is taking an intermediate-level French course.
B2 noun /ˌaɪ.səˈleɪ.ʃən/

Isolation

Meaning
the process or fact of isolating or being isolated; separation from other people or things
Example
The patient was kept in isolation to prevent the spread of the infectious disease.
C2 noun /ˌɪnkænˈdɛsəns/

incandescence

Meaning
the emission of light from a hot object; brilliance
Example
The incandescence of the candle filled the dark room.
C2 verb /ɪnˈtɜːr/

inter

Meaning
To bury a dead body in the ground.
Example
They decided to inter the soldier with full honors.
C1 adjective /ɪnˈflɛksəbl/

inflexible

Meaning
Not able to bend or change; unwilling to change ideas or behavior.
Example
His inflexible attitude made negotiations difficult.
C2 verb /ˌɪmpɔːrˈtuːn/

importune

Meaning
To ask someone persistently or pressingly for something
Example
The child importuned his mother for a new toy.
C2 adjective /ɪˈrɛfrəɡəbəl/

irrefragable

Meaning
Impossible to refute, deny, or break
Example
The lawyer presented irrefragable evidence that proved his client’s innocence.
B2 noun, verb /ˈɪnstɪˌtjuːt/

institute

Meaning
as a noun, an organization founded for a specific purpose; as a verb, to establish or initiate
Example
The university decided to institute new rules for the library.
B1 adjective /ɪnˈfɔːrməl/

Informal

Meaning
relaxed and friendly; not official or ceremonial; casual
Example
The meeting was informal and relaxed.
C1 adjective /ɪnˈsʌf.ər.ə.bəl/

insufferable

Meaning
Too extreme to bear; intolerable.
Example
The heat during the summer was insufferable.
C2 noun /ɪˈnænɪti/

inanity

Meaning
a nonsensical remark or action; silliness; emptiness
Example
The speech was full of inanities that bored the audience.
C1 verb /ˈaɪdəlaɪz/

idolize

Meaning
To admire or worship someone excessively.
Example
Fans often idolize celebrities for their talent and lifestyle.
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 adjective /ɪnˈfɜːm/

infirm

Meaning
Weak, especially due to old age or illness.
Example
The infirm old man needed assistance to walk.
C1 adjective /ˌɪrɪˈvɜːrsəbl/

irreversible

Meaning
Not able to be undone, changed, or reversed.
Example
The damage caused by the fire was irreversible.
C1 adjective /ˌɪn.dɪˈspen.sə.bəl/

indispensable

Meaning
Absolutely necessary, essential
Example
Water is indispensable for human survival.
B1 verb /ɪnˈvɑːlv/

involve

Meaning
to include as a necessary part, or to engage someone in an activity
Example
The project will involve several departments working together.
B2 adjective /ɪnˈtɛnsɪv/

intensive

Meaning
Involving a lot of effort, energy, or concentration in a short period of time.
Example
She attended an intensive English course before moving abroad.
B1 adjective /ɪnˈtɜːrnəl/

internal

Meaning
situated inside; relating to the inside or inner part of something
Example
The company is conducting an internal audit this month.