infestation
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C1 noun ˌɪnfɛsˈteɪʃən

infestation

Meaning
The presence of an unusually large number of insects or animals in a place, causing damage or disease.
Example
The infestation of ants in the kitchen led to immediate pest control measures.
C1 adjective /ɪnˈkɒŋɡruəs/

incongruous

Meaning
Not fitting in with or suitable for the surroundings.
Example
His jokes were incongruous during the serious meeting.
C1 adjective /ɪmˈprɒmp.tjuː/

impromptu

Meaning
Done without being planned, organized, or rehearsed; spontaneous.
Example
He gave an impromptu speech at the event.
C1 adjective /ɪnˈæk.tɪv/

Inactive

Meaning
not active; not working; dormant; idle
Example
The volcano has been inactive for over a century.
C1 noun /ˌɪnkɑːrˈneɪʃən/

incarnation

Meaning
the embodiment of a deity, spirit, or quality in a physical form
Example
The monk was considered the incarnation of compassion.
C1 verb /ɪmˈpɪndʒ/

impinge

Meaning
to have an effect or impact on something; to encroach or infringe
Example
The noise from the construction site impinges on our daily activities.
C1 adjective /ɪnˈdɪɡnənt/

indignant

Meaning
Feeling or showing anger at something considered unfair or unjust.
Example
She was indignant when accused of cheating.
C1 noun /ɪˌreɡjəˈlærɪti/

irregularity

Meaning
lack of regularity or consistency; a deviation from what is normal, expected, or orderly
Example
The audit revealed several financial irregularities in the company’s records.
C1 noun /ˌaɪ.diˈɒl.ə.dʒi/

ideology

Meaning
A system of ideas and ideals, especially one that forms the basis of economic or political theory and policy.
Example
Democracy is based on the ideology of freedom and equality.
C1 adjective /ˌɪn.ɪˈfɛk.tʃu.əl/

ineffectual

Meaning
Not producing any or the desired effect; lacking the ability or qualities to achieve a purpose.
Example
The manager’s ineffectual leadership caused the team to lose motivation.
C1 verb /ɪmˈpiːd/

impede

Meaning
To obstruct or hinder the progress or development of something.
Example
Lack of funds can impede business growth.
C1 adjective /ˌɪntərˈtʃeɪndʒəbl/

interchangeable

Meaning
able to be exchanged with each other without difference or loss of function
Example
These machine parts are interchangeable, so they can be replaced easily.
C1 noun /ˌɪm.pəˈzɪʃ.ən/

Imposition

Meaning
the action or process of imposing something or of being imposed; an unfair burden or demand
Example
The imposition of new taxes without consultation angered the citizens greatly.
C1 adjective /ɪˈnɔːɡjərəl/

Inaugural

Meaning
marking the beginning of something; first; opening
Example
The president delivered his inaugural speech.
C1 noun /ˌɪnsəˈfɪʃənsi/

insufficiency

Meaning
The state of not being enough or not being adequate.
Example
The project failed due to the insufficiency of funds.
C1 adjective /ˌɪndɪˈstrʌktəbl/

indestructible

Meaning
Impossible to destroy or break.
Example
The superhero's shield was said to be indestructible.
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 /ɪmˈpɛn.ɪ.trə.bəl/

impenetrable

Meaning
Impossible to pass through or enter; impossible to understand.
Example
The dense forest was nearly impenetrable.
C1 noun ˌɪn.ɪˈfɪʃ.ən.si

inefficiency

Meaning
The state or quality of not achieving maximum productivity; failure to make the best use of time or resources.
Example
Government inefficiency leads to slow project completion.
C1 adjective ˈɪn.tər.ɪm

interim

Meaning
In or for the intervening period; provisional or temporary.
Example
Interim governments manage transitional phases.
C1 adjective /ˌɪlɪˈdʒɪtɪmət/

illegitimate

Meaning
Not authorized by law, rules, or standards; not recognized as valid.
Example
The court ruled the contract to be illegitimate.
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 ɪnˌten.sɪ.fɪˈkeɪ.ʃən

intensification

Meaning
The process of becoming or making something more intense or extreme.
Example
The intensification of climate change requires urgent action.
C1 noun /ɪnˈsɜːrdʒənt/

insurgent

Meaning
A person who rises in revolt against authority or government.
Example
The army arrested several insurgents after the attack.
C1 noun /ˈɪntrɪkəsi/

intricacy

Meaning
the quality of being very detailed or complicated
Example
The intricacy of the design impressed everyone.
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 noun /ˌɪndɪɡˈneɪʃən/

indignation

Meaning
Strong displeasure or anger caused by something unjust, offensive, or insulting.
Example
Public indignation grew after the unfair verdict.
C1 adjective /ɪnˈdʌldʒənt/

indulgent

Meaning
Having a tendency to be overly generous or lenient with someone.
Example
The indulgent mother allowed her child to stay up late.
C1 noun /ɪmˈpɛd.ɪ.mənt/

impediment

Meaning
A hindrance or obstruction in doing something; something that prevents progress.
Example
Lack of funds is a major impediment to the project.
C1 noun /ˈɪŋ.krə.mənt/

Increment

Meaning
an increase or addition, especially one of a series on a fixed scale; a regular increase in salary
Example
He received an annual increment of five percent in his salary this year.
C1 adjective /ˌɪndɪˈstɪŋkt/

indistinct

Meaning
Not clear or sharply defined; vague or blurred.
Example
The sound of voices was indistinct in the distance.
C1 adjective /ˌɪnækˈsɛsəbl/

inaccessible

Meaning
unable to be reached, entered, or understood
Example
The remote village is almost inaccessible during the rainy season.
C1 verb /ˌɪntəˈsɛkt/

intersect

Meaning
to cross or pass through each other
Example
The two roads intersect at the city center.
C1 adjective /ɪmˈpɜːrtɪnənt/

impertinent

Meaning
rude and showing a lack of respect
Example
It was impertinent of him to question the manager's decision.
C1 verb /ɪmˈpɛl/

impel

Meaning
to drive, force, or urge someone to do something
Example
Her curiosity impelled her to open the mysterious box.
C1 adjective /ɪnˈsɪdiəs/

insidious

Meaning
Proceeding in a gradual, subtle way but with harmful effects.
Example
The insidious spread of misinformation can damage trust.
C1 adjective /ˌɪnəˈfɛnsɪv/

inoffensive

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

impoverish

Meaning
To make someone poor or reduce the quality or richness of something.
Example
The long war impoverished the entire nation.
C1 adjective /ɪˈlɪsɪt/

illicit

Meaning
Forbidden by law, rules, or custom.
Example
The police shut down the illicit drug operation.
C1 adjective /ɪnˈhɪbɪtɪd/

inhibited

Meaning
Unable to act in a relaxed and natural way, especially due to self-consciousness or restraint.
Example
He was too inhibited to express his true feelings.
C1 adjective /ˌɪnɪkˈsplɪkəbl/

inexplicable

Meaning
Impossible to explain or understand.
Example
The sudden disappearance of the file was inexplicable.
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.
C1 noun /ɪnˈsɜːrdʒəns/

insurgence

Meaning
An act of rebellion or uprising against authority.
Example
The government struggled to contain the growing insurgence.
C1 adjective /ˈɪnərmoʊst/

Innermost

Meaning
most private and secret; deepest; most personal
Example
She shared her innermost feelings with her closest friend.
C1 adjective ˈɪn.lənd

Inland

Meaning
Situated in the interior of a country; away from the coast.
Example
Inland transport boosts local trade.
C1 adjective ɪˈneɪt

Innate

Meaning
Existing from birth or natural
Example
She has an innate talent for music.
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 /ˌɪntərˈtwaɪnd/

intertwined

Meaning
closely connected or twisted together
Example
Their lives became deeply intertwined after the accident.
C1 adjective /ɪmˈpɑːrʃəl/

Impartial

Meaning
treating all sides fairly; unbiased; neutral
Example
A good judge must remain impartial throughout the trial.
C1 verb /ɪmˈpiːtʃ/

impeach

Meaning
To charge a public official with misconduct while in office.
Example
The parliament voted to impeach the president.
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.
C1 adjective /ɪnˈɔːdəbl/

inaudible

Meaning
Unable to be heard.
Example
Her voice was almost inaudible over the noise.
C1 verb /ɪnˈvɪɡ.ər.eɪt/

invigorate

Meaning
To give strength or energy to someone or something.
Example
A morning walk can invigorate both body and mind.
C1 noun /ˈɪm.pæs/

impasse

Meaning
A situation where no progress is possible.
Example
The negotiations reached an impasse, delaying the agreement.
C1 adjective /ɪˈniː.bri.eɪ.tɪd/

inebriated

Meaning
under the influence of alcohol; drunk
Example
He stumbled into the room completely inebriated.
C1 noun /ˌɪntərˈmiːdiˌɛri/

intermediary

Meaning
A person who acts as a link between people in order to try to bring about an agreement; a mediator.
Example
The diplomat served as an intermediary between the two conflicting nations.
C1 adjective /ɪmˈpæʃənd/

impassioned

Meaning
Filled with or showing great emotion.
Example
She gave an impassioned speech about human rights.
C1 adjective /ɪˈmjuː.tə.bəl/

immutable

Meaning
Unchangeable, permanent, or fixed
Example
The laws of physics are considered immutable.
C1 verb /ɪnˈfjʊərieɪt/

infuriate

Meaning
To make someone extremely angry.
Example
His careless remarks infuriated the entire team.
C1 noun /ˌɪməˈrælɪti/

immorality

Meaning
the quality of being immoral; behavior that violates accepted moral standards
Example
The community condemned the immorality of the corrupt officials.
C1 adjective /ɪnˈfɜːm/

infirm

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

inquisition

Meaning
A prolonged and intense questioning or investigation, often harsh in nature.
Example
The journalist faced an inquisition from the panel about his sources.
C1 adjective /ɪnˈsʌf.ər.ə.bəl/

insufferable

Meaning
Too extreme to bear; intolerable.
Example
The heat during the summer was insufferable.
C1 adjective /ɪˈlʌstriəs/

illustrious

Meaning
Well known, respected, and admired for past achievements.
Example
She had an illustrious career in medicine.
C1 adjective /ˈɜːrksəm/

irksome

Meaning
annoying or irritating
Example
Waiting in a long line is one of the most irksome tasks.
C1 noun ˌɪnsjʊˈleɪʃən

insulation

Meaning
Material used to prevent heat, sound, or electricity from being transmitted from one area to another.
Example
Insulation of food storage areas can prevent pests from entering.
C1 noun /aɪˈtɪnərɛri/

itinerary

Meaning
A planned route or schedule of a journey or trip.
Example
The travel agent gave us a detailed itinerary for our vacation.
C1 noun /ɪnˈsek.tɪ.saɪd/

Insecticide

Meaning
a substance used for killing insects; a chemical pesticide that targets insects
Example
The farmer sprayed insecticide on his crops to protect them from harmful bugs.
C1 adjective /ˌɪndɪˈskrɪmɪnət/

indiscriminate

Meaning
Done without careful judgment; random or haphazard.
Example
The indiscriminate use of pesticides harms the environment.
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.
C1 noun /ɪmˈbæl.əns/

Imbalance

Meaning
lack of proportion or relation between corresponding things; unequal distribution
Example
The doctor said the patient's dizziness was caused by an inner ear imbalance.
C1 adjective ˌɪm.pəˈsɛp.tɪ.bəl

imperceptible

Meaning
So subtle or gradual that it is difficult to notice or perceive
Example
The changes in his behavior were imperceptible at first.
C1 noun /ˌɪn.dɪˈsɪʒ.ən/

Indecision

Meaning
the inability to make decisions quickly; uncertainty about what to do
Example
Her indecision about which job offer to accept caused her to miss both opportunities.
C1 adjective /ɪnˈdʒʊəriəs/

injurious

Meaning
Causing or likely to cause harm or damage.
Example
Smoking is injurious to health.
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.
C1 noun /ˌɪməˈtjʊərəti/

immaturity

Meaning
the state of not being fully developed emotionally, mentally, or physically; lack of maturity
Example
His immaturity made it difficult for him to handle responsibility.
C1 adjective /ɪnˈkrɛdjələs/

incredulous

Meaning
unwilling or unable to believe something
Example
He gave her an incredulous look when she claimed she could fly.
C1 adjective /ɪnˈsɒlvənt/

insolvent

Meaning
unable to pay debts owed
Example
The insolvent firm could not meet its financial obligations.
C1 adverb /ˌɪn.ədˈvɜːr.tənt.li/

Inadvertently

Meaning
without being aware of what you are doing; unintentionally; by mistake
Example
She inadvertently deleted the important file while cleaning her computer.
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 /ɪˈnɔːrdənət/

inordinate

Meaning
Excessive or unusually large in degree.
Example
She spent an inordinate amount of time on her phone.
C1 adverb /ˌɪnsɪˈdɛntəli/

incidentally

Meaning
by the way; used to introduce a remark not directly related to the main subject
Example
Incidentally, did you know that she studied in Paris?
C1 adjective /ɪnˈstɪŋk.tɪv/

instinctive

Meaning
Based on instinct; done without conscious thought; natural and automatic.
Example
His instinctive reaction saved his life.
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.
C1 adjective /ɪnˈflɛksəbl/

inflexible

Meaning
Not able to bend or change; unwilling to change ideas or behavior.
Example
His inflexible attitude made negotiations difficult.
C1 adjective /ˌɪrɪˈvɜːrsəbl/

irreversible

Meaning
Not able to be undone, changed, or reversed.
Example
The damage caused by the fire was irreversible.
C1 adjective /ˈɪmpjəd(ə)nt/

impudent

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

intestine

Meaning
The part of the digestive system where food is digested and absorbed, extending from the stomach to the anus.
Example
The doctor explained how nutrients are absorbed in the small intestine.
C1 verb /ˈɪmplɪˌkeɪt/

implicate

Meaning
To show someone’s involvement in a crime or wrongdoing.
Example
The evidence implicated several officials in the scandal.
C1 adjective /ɪˈnɒkjuəs/

innocuous

Meaning
Not harmful or offensive.
Example
His remark was completely innocuous and not meant to offend anyone.
C1 adjective /ɪnˈkwɪzɪtɪv/

inquisitive

Meaning
Curious or eager to learn and ask questions.
Example
The inquisitive child asked endless questions about the stars.
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 /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.
C1 adjective /ɪnˈkɒmpɪtənt/

incompetent

Meaning
Lacking the necessary ability or skills to do something successfully.
Example
He was fired because he was incompetent at his job.
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.
C1 noun ɪmˈpɛə(r)mənt

impairment

Meaning
The state of being damaged or weakened; a disability or handicap.
Example
Hearing impairment can be caused by long-term exposure to loud noise.
C1 noun /ˌɪrɪˌspɒnsəˈbɪləti/

irresponsibility

Meaning
lack of responsibility or accountability; failure to act in a reliable or sensible way
Example
The accident was caused by his irresponsibility at work.
C1 noun /ɪnˈdɪɡ.nə.ti/

Indignity

Meaning
treatment or circumstances that cause one to feel shame or loss of dignity; humiliation
Example
She refused to suffer the indignity of being searched without proper cause.
C1 adjective /ˌɪnkənˈsiːvəbl̩/

inconceivable

Meaning
Impossible to imagine or believe; beyond comprehension.
Example
It seemed inconceivable that she could finish the marathon after such little training.
C1 noun /ˌɪnsɪɡˈnɪfɪkəns/

insignificance

Meaning
The quality of being unimportant or trivial.
Example
He felt a sense of insignificance in the vast universe.
C1 adjective /ɪnˈsteɪbəl/

instable

Meaning
not stable; liable to change, collapse, or fail; lacking firmness or reliability
Example
The instable political situation worried foreign investors.
C1 noun ˈɪn.fər.əns

inference

Meaning
A conclusion reached on the basis of evidence and reasoning; logical deduction.
Example
Scientists make inferences based on experimental data.
C1 adjective /ˌɪn.səbˈstæn.ʃəl/

insubstantial

Meaning
Lacking strength, substance, or solidity.
Example
The evidence provided was insubstantial and unconvincing.
C1 noun /ɪnˈækjʊrəsi/

inaccuracy

Meaning
lack of accuracy or precision; an incorrect or wrong detail
Example
The report contained several factual inaccuracies.
C1 adjective /ɪmˈplɔːzəbl/

implausible

Meaning
Not seeming reasonable or probable; unlikely to be true.
Example
The story she told was so implausible that no one believed her.
C1 adjective /ɪˈmuː.və.bəl/

immovable

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

intricate

Meaning
very detailed, complex, and difficult to understand
Example
The artist created an intricate pattern on the wall.
C1 noun /ɪmˈpɛdɪmənt/

impediments

Meaning
A hindrance or obstruction in doing something; things that prevent progress or achievement.
Example
Economic impediments often hinder social development.
C1 verb /ɪnˈdaɪt/

indict

Meaning
to formally accuse someone of committing a serious crime
Example
The grand jury decided to indict the politician for corruption.
C1 adjective /ˌɪntəˈrɑːɡətɪv/

interrogative

Meaning
Relating to or conveying a question; in grammar, used to form questions.
Example
She raised an interrogative eyebrow when she heard the news.
C1 adjective ɪnˈdʒiː.ni.əs

ingenious

Meaning
Showing inventiveness and skill; clever, original, and inventive.
Example
His ingenious ideas transformed modern physics.
C1 noun ˈɪm.pɪ.təs

impetus

Meaning
The force or motivation that drives something forward; momentum.
Example
The new policy provided an impetus for economic growth.
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 /ˌɪnkjʊˈbeɪʃən/

incubation

Meaning
the process of keeping eggs, cells, or organisms in the right conditions for development
Example
The incubation of the eggs lasted for three weeks.
C1 adjective /ɪˈneɪn/

inane

Meaning
lacking sense, meaning, or significance; silly or pointless
Example
The movie was criticized for its inane dialogue.
C1 verb /ɪmˈbɛd/

imbed

Meaning
To fix firmly or deeply in a surrounding mass.
Example
The journalist imbedded himself with the troops to report firsthand.
C1 noun /ˌɪnˈdɪsəplɪn/

indiscipline

Meaning
lack of discipline or self-control; failure to obey rules or maintain order
Example
Indiscipline among the students disrupted the learning environment.
C1 noun /ɪnˈfɜːrnoʊ/

inferno

Meaning
a large, intense fire that is dangerously out of control
Example
The building turned into an inferno within minutes.