Insomnia
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C1 noun /ɪnˈsɒm.ni.ə/

Insomnia

Meaning
habitual sleeplessness; inability to sleep; the condition of being unable to sleep
Example
Her chronic insomnia made it difficult for her to concentrate during work hours.
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.
C1 noun /ˈɪn.tə.mə.si/

Intimacy

Meaning
close familiarity or friendship; closeness; a private cozy atmosphere
Example
The couple valued the emotional intimacy they shared more than material possessions.
C1 adjective /ˌɪndɪˈsaɪsɪv/

Indecisive

Meaning
unable to make decisions quickly; hesitant; wavering
Example
She was indecisive about which university to attend.
C1 adjective /ɪnˈtjuː.ɪ.tɪv/

intuitive

Meaning
Based on instinctive understanding rather than reasoning.
Example
The software has an intuitive design that makes it easy to use.
C1 noun /ˌɪmɔːrˈtæləti/

immortality

Meaning
the state of living forever; eternal life or lasting fame beyond death
Example
Many ancient cultures believed that heroes could achieve immortality through great deeds.
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 /ɪmˈpɛndɪŋ/

impending

Meaning
about to happen soon, usually something unpleasant or threatening
Example
The villagers were worried about the impending flood.
C1 adjective /ɪˈræʃənəl/

irrational

Meaning
not logical or reasonable; lacking clear thought
Example
His fear of the dark was completely irrational.
C1 noun /ɪˌluːmɪˈneɪʃən/

illumination

Meaning
the act of lighting something or making something clear
Example
The street was filled with bright illumination from the lamps.
C1 adjective /ˌɪnəˈfɛnsɪv/

inoffensive

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

instigate

Meaning
To bring about or initiate an action, often something negative.
Example
He was accused of instigating the riot.
C1 adjective /ɪˈnɜːrt/

inert

Meaning
lacking the ability or strength to move or act; chemically inactive
Example
The patient remained inert on the bed.
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 verb /ˈaɪdəlaɪz/

idolize

Meaning
To admire or worship someone excessively.
Example
Fans often idolize celebrities for their talent and lifestyle.
C1 adjective /ɪˈnɛpt/

inept

Meaning
lacking skill or ability; clumsy or incompetent
Example
His inept handling of the situation made it worse.
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.
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 /ɪˈlʌstriəs/

illustrious

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

impasse

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

inexplicable

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

implode

Meaning
To collapse or burst inward violently.
Example
The old building imploded during the demolition.
C1 noun /ˈɪn.floʊ/

inflow

Meaning
The movement of things such as money, people, or water into a place.
Example
The inflow of tourists boosted the local economy.
C1 noun /ɪmˌpɜː.sənˈeɪ.ʃən/

impersonation

Meaning
The action of pretending to be another person for the purpose of entertainment or fraud.
Example
Online impersonation is a serious cybercrime.
C1 adjective /ɪmˈprɒmp.tjuː/

impromptu

Meaning
Done without being planned, organized, or rehearsed; spontaneous.
Example
He gave an impromptu speech at the event.
C1 noun ɪnˈsɛpʃən

inception

Meaning
The establishment or starting point of an institution or activity.
Example
The inception of the company marked a new era in the industry.
C1 adjective /ɪnˈhɛrənt/

inherent

Meaning
Existing in something as a natural, permanent, or essential quality.
Example
There are inherent risks in extreme sports.
C1 adjective ˌɪn.krəˈmen.təl

incremental

Meaning
Relating to or denoting an increase or addition, especially one of a series on a fixed scale; proceeding in small stages.
Example
Incremental changes ensure sustainability.
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 /ˈɪnstɪˌɡeɪtər/

instigator

Meaning
A person who brings about or initiates something, usually something bad.
Example
The police identified him as the instigator of the violence.
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 /ˈɪnkjʊˌbeɪtər/

incubator

Meaning
a device or environment that provides suitable conditions for eggs, cells, or infants to develop
Example
The premature baby was placed in an incubator for care.
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 adjective /ɪnˈdʌktɪv/

inductive

Meaning
characterized by the inference of general laws from particular instances; reasoning from specific cases to general principles
Example
The scientist used inductive reasoning to form a hypothesis.
C1 noun /ˌɪn.səˌbɔːr.dɪˈneɪ.ʃən/

insubordination

Meaning
Defiance of authority; refusal to obey orders.
Example
The soldier was punished for insubordination during the mission.
C1 adjective /ɪˈlɪsɪt/

illicit

Meaning
Forbidden by law, rules, or custom.
Example
The police shut down the illicit drug operation.
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.
C1 noun ˌɪrɪˈvɜːrsəbl ˈdæmɪdʒ

irreversible damage

Meaning
Harm or injury that cannot be undone or repaired.
Example
Climate change causes irreversible damage to ecosystems.
C1 verb /ɪnˈterəˌɡeɪt/

interrogate

Meaning
to ask someone questions in a thorough and formal way; to question intensively
Example
The police interrogated the suspect for hours.
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.
C1 adjective /ɪmˈpʌlsɪv/

impulsive

Meaning
acting suddenly without careful thought
Example
She made an impulsive decision to buy the car.
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 /ɪmˈpjʊər/

Impure

Meaning
contaminated; not clean; mixed with foreign substances
Example
The impure water caused health problems in the village.
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 /ɪnˈflæməˌtɔːri/

inflammatory

Meaning
causing inflammation in the body; arousing anger, hostility, or strong emotion
Example
His inflammatory speech triggered protests across the city.
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 /ˌɪntərˈtwaɪnd/

intertwined

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

indictment

Meaning
a formal charge or accusation of a serious crime
Example
The indictment accused the company of multiple violations.
C1 adjective /ˌɪnədˈmɪsəbl̩/

inadmissible

Meaning
Not allowed, especially as evidence in a court of law.
Example
The judge ruled the evidence inadmissible.
C1 adjective /ɪˈmoʊbəl/

immobile

Meaning
unable to move or be moved
Example
After the accident, he was immobile for weeks.
C1 noun /ˌɪnækˈtɪvɪti/

inactivity

Meaning
the state of not being active physically or mentally; lack of action
Example
Prolonged inactivity can negatively affect both physical and mental health.
C1 verb /ˈɪrɪˌɡeɪt/

irrigate

Meaning
to supply water to land or crops; to wash out a wound with water
Example
Farmers irrigate their fields during dry seasons.
C1 noun/verb /ˈɪnsɛns/

incense

Meaning
a substance burned for its sweet smell (noun); to make very angry (verb)
Example
The smell of incense filled the temple, but his rude words incensed her.
C1 adjective /ɪnˈdʒʊəriəs/

injurious

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

Indifference

Meaning
lack of interest, concern, or sympathy; the state of not caring about something
Example
His indifference to his studies resulted in poor grades throughout the semester.
C1 adjective /ˌɪnədˈvɜːrtənt/

inadvertent

Meaning
Not resulting from or achieved through deliberate planning; unintentional.
Example
Her inadvertent mistake caused a delay in the project.
C1 noun /ɪnˈsæn.ə.ti/

Insanity

Meaning
the state of being seriously mentally ill; extreme foolishness or irrationality
Example
The defense lawyer argued that his client was not guilty by reason of insanity.
C1 adjective ɪˈluː.sər.i

illusory

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

infuse

Meaning
to fill or spread through something; to instill a quality, idea, or feeling
Example
The teacher tried to infuse her students with a love for reading.
C1 adjective /ˌɪnhɒˈspɪtəbl/

inhospitable

Meaning
Harsh and difficult to live in; unfriendly or unwelcoming to guests.
Example
The desert is an inhospitable environment for most plants.
C1 adjective ˌɪn.trəˈspek.tɪv

introspective

Meaning
Characterized by or given to introspection; examining one's own thoughts and feelings.
Example
Writers tend to be highly introspective individuals.
C1 adjective ˌɪn.təˈstel.ər

interstellar

Meaning
Occurring or situated between stars.
Example
Scientists study interstellar travel possibilities.
C1 verb /ˌɪntəˈsɛkt/

intersect

Meaning
to cross or pass through each other
Example
The two roads intersect at the city center.
C1 adjective ɪn ˈfleɪ.ʃə.ner.i

inflationary

Meaning
Characterized by or tending to cause monetary inflation; relating to rising prices.
Example
The government took measures to control inflationary pressures.
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 /ɪmˈpɛtʃ.u.əs/

impetuous

Meaning
Acting or done quickly and without thought or care; impulsive.
Example
His impetuous decision led to unexpected consequences.
C1 adjective /ɪˈmeʒərəbəl/

Immeasurable

Meaning
too large or extensive to measure; boundless
Example
The immeasurable love of a mother knows no bounds.
C1 adverb /ˈɪnwərdli/

inwardly

Meaning
In the mind or spirit; not outwardly visible.
Example
She smiled outwardly but inwardly she was worried.
C1 adjective /ɪnˈvɪnsəbl/

invincible

Meaning
too powerful to be defeated or overcome
Example
The team seemed invincible after winning ten matches in a row.
C1 adjective ɪnɪɡˈzɔːstɪbəl

inexhaustible

Meaning
Unable to be used up or worn out; limitless.
Example
His inexhaustible energy allowed him to work tirelessly on his projects.
C1 adjective ˈɪn.lənd

Inland

Meaning
Situated in the interior of a country; away from the coast.
Example
Inland transport boosts local trade.
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 ɪnˈkʌm.bənt

incumbent

Meaning
necessary for (someone) as a duty or responsibility.
Example
It is incumbent upon all citizens to obey the law.
C1 noun /ˈɪnlɛt/

inlet

Meaning
A small arm of the sea, a lake, or a river; an opening or passage for entry.
Example
The boat entered a narrow inlet along the coast.
C1 adjective /ɪnˈkɒmp(ə)rəbl/

incomparable

Meaning
Without an equal in quality or excellence; matchless.
Example
The view from the mountain was incomparable.
C1 adjective /ɪnˈtɜːrmənəbl/

interminable

Meaning
Seemingly endless; having no apparent end.
Example
The meeting felt interminable and exhausting.
C1 noun ˌɪn.tuˈɪʃ.ən

intuition

Meaning
The ability to understand something immediately, without the need for conscious reasoning.
Example
Her intuition told her something was wrong.
C1 noun /ˌɪnkənˈsɪstənsi/

inconsistency

Meaning
The quality of being contradictory, irregular, or not staying the same.
Example
There is an inconsistency between his words and actions.
C1 adjective /ˈɪnərmoʊst/

Innermost

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

intimidation

Meaning
The action of frightening or threatening someone to make them do something.
Example
The workers reported cases of intimidation by the management.
C1 adjective /ˈɪnsjələr/

insular

Meaning
Narrow-minded, isolated, or relating to an island.
Example
The community was criticized for its insular attitudes toward outsiders.
C1 adjective; noun /ɪˈmɔːrtl/

immortal

Meaning
living forever; never dying; lasting forever in fame or memory
Example
Legends often describe heroes as immortal beings who never die.
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 /ˌɪnkənˈsɪdərət/

inconsiderate

Meaning
Thoughtless; showing a lack of concern for others.
Example
It was inconsiderate of him to play loud music late at night.
C1 adjective /ɪˈluː.sɪv/

Illusive

Meaning
deceptive; appearing to exist but not real; misleading
Example
The promise of easy money proved to be illusive and misleading.
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 (plural) /ˈɪndɪˌsiːz/

indices

Meaning
plural form of index; statistical measures or reference points used for comparison
Example
Stock market indices fell sharply after the announcement.
C1 adjective /ɪˈlɒdʒ.ɪ.kəl/

Illogical

Meaning
not reasonable or sensible; lacking logic
Example
It would be illogical to go swimming in such cold weather.
C1 adjective /ˌɪnækˈsɛsəbl/

inaccessible

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

Inborn

Meaning
existing from birth; natural; inherent
Example
She has an inborn talent for music.
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 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.səˈbɔːr.dɪ.nət/

insubordinate

Meaning
Defiant of authority; disobedient to orders.
Example
The insubordinate employee refused to follow the manager's instructions.
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 adjective /ɪˈrɛpərəbəl/

Irreparable

Meaning
impossible to repair or fix; permanent damage that cannot be undone
Example
The accident caused irreparable damage to his spine.
C1 adjective /ɪˈnænɪmət/

inanimate

Meaning
not alive, especially not in the manner of animals and humans; lifeless
Example
The museum was full of inanimate objects from ancient times.
C1 noun /ɪnˈdʒʌŋkʃən/

injunction

Meaning
A judicial order restraining a person from an action or compelling a certain act.
Example
The court issued an injunction to stop the company from polluting the river.
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 noun /ˈɪn.trə.vɜːrt/

introvert

Meaning
A person who tends to be shy and prefers spending time alone rather than in groups.
Example
As an introvert, he preferred reading over attending parties.
C1 adjective /ɪnˈsɛp(ə)rəbəl/

inseparable

Meaning
Unable to be separated or always together.
Example
The two friends have been inseparable since childhood.
C1 adjective /ˈɪmpətənt/

impotent

Meaning
Lacking power, ability, or strength to take effective action.
Example
The citizens felt impotent against the corrupt system.
C1 adjective /ˈɪnfəməs/

infamous

Meaning
well known for some bad quality or deed
Example
The dictator was infamous for his cruelty.
C1 noun /ɪmˈpɜː.mə.nəns/

impermanence

Meaning
The state or fact of lasting for only a limited period of time.
Example
The philosophy of Buddhism emphasizes the impermanence of life.
C1 noun ɪnˌɛv.ɪ.təˈbɪl.ɪ.ti

inevitability

Meaning
The quality of being certain to happen and impossible to avoid or prevent.
Example
The inevitability of change is a part of life.
C1 noun /ɪnˈsɜːrdʒəns/

insurgence

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

Impostor

Meaning
a person who pretends to be someone else in order to deceive others; a fraud
Example
The impostor convinced everyone he was a doctor until his fake credentials were discovered.
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 ˌɪn.təˈdɪs.ɪ.plɪ.nər.i

interdisciplinary

Meaning
Relating to more than one branch of knowledge.
Example
The interdisciplinary approach in education enhances problem-solving skills.
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 adjective /ˌɪnədˈvaɪzəbl/

inadvisable

Meaning
Not recommended; likely to have undesirable consequences.
Example
It is inadvisable to drive in such heavy rain.
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.
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 verb /ɪnˈkɑːrsəreɪt/

incarcerate

Meaning
to imprison or confine someone
Example
The authorities incarcerated the criminal after the trial.
C1 adjective ˌɪn.təˈmɪt.ənt

intermittent

Meaning
Happening irregularly, not continuously.
Example
The rain was intermittent throughout the day.
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 /ɪˈnɔːrdənət/

inordinate

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

imminence

Meaning
the state of being about to happen
Example
The imminence of the storm forced people to take shelter.
C1 verb ɪˈnɔː.ɡjə.reɪ.tɪd

inaugurated

Meaning
Begin or introduce (a system, policy, or period) formally.
Example
The organization was inaugurated officially.