infiltration
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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 /ˈɪŋklɪŋ/

inkling

Meaning
A slight idea, hint, or suspicion about something.
Example
She had an inkling that he was planning a surprise.
C1 adjective ɪnˈdʒiː.ni.əs

ingenious

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

indulgence

Meaning
The practice of allowing oneself to enjoy the pleasure of something.
Example
His indulgence in junk food affected his health.
C1 adjective /ɪmˈpæsɪv/

impassive

Meaning
Not showing or feeling emotion; expressionless.
Example
Despite the shocking news, she remained impassive.
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 /ˌɪrɪˈspɛktɪv/

Irrespective

Meaning
without taking something into account; regardless of
Example
All students will be treated equally, irrespective of their background.
C1 adjective /ˌɪnkəmˈpætəbl/

incompatible

Meaning
Not able to exist or work together without conflict.
Example
Their personalities were completely incompatible.
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 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 /ˌɪndɪˈstɪŋkt/

indistinct

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

Indecisive

Meaning
unable to make decisions quickly; hesitant; wavering
Example
She was indecisive about which university to attend.
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 /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 verb /ɪnˈvɜːrt/

invert

Meaning
To turn something upside down or in the opposite position, order, or direction.
Example
He inverted the glass to let the water drain out.
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 adjective /ˈɪnsjələr/

insular

Meaning
Narrow-minded, isolated, or relating to an island.
Example
The community was criticized for its insular attitudes toward outsiders.
C1 adverb ɪnˈtrɪn.zɪ.kli

intrinsically

Meaning
In a way that is naturally or inherently part of something's essential nature.
Example
Some people are intrinsically motivated to learn.
C1 noun ˌɪm.pʌlˈsɪv.ɪ.ti

impulsivity

Meaning
The tendency to act quickly and without thought or care; lack of self-control.
Example
His impulsivity led him to make reckless choices.
C1 adjective /ˈɜːrksəm/

irksome

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

indignation

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

industrious

Meaning
Hardworking and diligent in one's duties.
Example
She is an industrious student who always completes her assignments on time.
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.
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 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 noun ˌɪntədɪˈpɛndənsi

interdependency

Meaning
The dependence of two or more people or things on each other.
Example
The interdependency of the countries led to greater cooperation.
C1 noun /ˌɪnɪkˈspɪəriəns/

inexperience

Meaning
Lack of knowledge or skill in a particular activity or field.
Example
His inexperience in handling negotiations was evident.
C1 adjective /ɪˈneɪn/

inane

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

ingrained

Meaning
Firmly fixed or established; deeply rooted and difficult to change.
Example
His ingrained habits were hard to break.
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 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 /ˌɪn.trəˈvɜːr.ʒən/

introversion

Meaning
The tendency to be inward-looking and shy, preferring solitary activities.
Example
Her introversion made it difficult for her to enjoy large parties.
C1 adjective /ɪnˈedəbəl/

Inedible

Meaning
not suitable or safe for eating; not edible
Example
The mushrooms were poisonous and completely inedible.
C1 adjective /ˌɪmprɪˈsaɪs/

imprecise

Meaning
Not exact or accurate; vague.
Example
His explanation was too imprecise to be helpful.
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 /ɪnˈsɜːrdʒəns/

insurgence

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

illegitimate

Meaning
Not authorized by law, rules, or standards; not recognized as valid.
Example
The court ruled the contract to be illegitimate.
C1 adverb, adjective /ˌɪnkɑːɡˈniːtoʊ/

incognito

Meaning
In disguise or with one's identity concealed.
Example
The celebrity traveled incognito to avoid the paparazzi.
C1 noun /ɪnˈkɒmpɪtəns/

incompetence

Meaning
Lack of ability, skill, or effectiveness in doing something.
Example
The project failed due to the manager’s incompetence.
C1 adjective /ˌɪndɪˈskraɪbəbəl/

Indescribable

Meaning
impossible to describe or express in words; beyond description
Example
The beauty of the sunset was indescribable.
C1 adjective /ˌɪndɪˈspjuːtəbəl/

Indisputable

Meaning
impossible to deny or argue against; undeniable; certain
Example
The evidence against him was indisputable.
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 adjective /ɪnˈdɪɡnənt/

indignant

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

indefensible

Meaning
not able to be protected or justified
Example
The minister’s remarks were considered indefensible by the public.
C1 adjective /ɪmˈpoʊzɪŋ/

imposing

Meaning
having an appearance that is grand, impressive, or commanding
Example
The castle is an imposing structure overlooking the valley.
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.
C1 verb /ɪmˈplɔːr/

implore

Meaning
To beg someone earnestly or desperately to do something.
Example
She implored him to stay with her.
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 noun /ˌɪnkoʊˈhɪrəns/

incoherence

Meaning
The quality of being unclear, confused, or lacking logical connection.
Example
His speech was full of incoherence and difficult to follow.
C1 adjective /ɪmˈpæsəbəl/

impassable

Meaning
Impossible to travel along or over.
Example
The road became impassable after the heavy snowfall.
C1 noun/verb /ˈɪmprɪnt/

imprint

Meaning
A mark or impression made by pressure; to establish or fix firmly in someone's mind.
Example
The event left an indelible imprint on the city's history.
C1 noun /ɪmˌpɒsəˈbɪlɪti/

impossibility

Meaning
the state or fact of being impossible; something that cannot be done or achieved
Example
Finishing the project in one day was an impossibility.
C1 adjective /ɪˈlʌstriəs/

illustrious

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

instructive

Meaning
useful and informative; providing knowledge or instruction
Example
The lecture was highly instructive and engaging.
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 /ɪnˈfleɪtɪd/

inflated

Meaning
excessively increased in size, value, or importance; filled with air or gas
Example
The company faced criticism for its inflated prices.
C1 adjective /ɪnˈtɛlɪdʒəbl/

intelligible

Meaning
Able to be understood; clear enough to be comprehended.
Example
Her speech was barely intelligible over the noise.
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 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 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 noun /ˌɪnkəmˈpliːtnəs/

incompleteness

Meaning
the state of not being complete or whole; lack of necessary parts or fullness
Example
The incompleteness of the report caused delays in the project.
C1 adjective /ˈɪnbɔːrn/

Inborn

Meaning
existing from birth; natural; inherent
Example
She has an inborn talent for music.
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 adjective /ɪmˈpɜːrtɪnənt/

impertinent

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

imagery

Meaning
visually descriptive or figurative language, especially in a literary work
Example
The poet's use of imagery brought the scene to life.
C1 adjective /ɪˈmeʒərəbəl/

Immeasurable

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

incite

Meaning
to provoke; to stir up
Example
His speech incited the crowd to violence.
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 ˈɪn.tər.ɪm

interim

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

indefinitely

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

irritant

Meaning
something that causes irritation or discomfort
Example
Dust is a common irritant for people with allergies.
C1 adjective /ɪmˈpæʃənd/

impassioned

Meaning
Filled with or showing great emotion.
Example
She gave an impassioned speech about human rights.
C1 adjective ɪˈneɪt

Innate

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

inexplicable

Meaning
Impossible to explain or understand.
Example
The sudden disappearance of the file was inexplicable.
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 /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 adjective /ɪnˈdiːsənt/

indecent

Meaning
not conforming to accepted standards of behavior or morality; improper or offensive
Example
He was warned for making an indecent remark during the meeting.
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 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 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 adjective /ɪnˈstɪŋk.tɪv/

instinctive

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

inebriated

Meaning
under the influence of alcohol; drunk
Example
He stumbled into the room completely inebriated.
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.
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.
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 adjective /aɪˈreɪt/

irate

Meaning
Extremely angry.
Example
The customer became irate after waiting for hours.
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 /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 verb /ɪnˈfjʊərieɪt/

infuriate

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

infrequent

Meaning
Happening rarely or not often.
Example
He made infrequent visits to his hometown after moving abroad.
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 /ɪˈrɛlɪvənsi/

irrelevancy

Meaning
the state of being unrelated or unimportant to the matter at hand
Example
The judge dismissed the argument because of its irrelevancy to the case.
C1 adjective /ˌaɪdiəˈlɪstɪk/

Idealistic

Meaning
pursuing high principles or ideals; unrealistically optimistic
Example
She has an idealistic view of changing the world.
C1 adjective /ɪnˈdetɪd/

Indebted

Meaning
owing money or gratitude to someone; obligated; grateful
Example
I am deeply indebted to my teacher for all her guidance.
C1 noun /ˌɪntərˈmɪʃən/

intermission

Meaning
A pause or break, especially during a performance or event.
Example
The play had a twenty-minute intermission.
C1 verb /ɪnˈskraɪb/

inscribe

Meaning
to write or carve words or symbols on a surface
Example
They inscribed her name on the trophy.
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 /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 /ˌɪntɪˈmeɪʃən/

intimation

Meaning
A subtle or indirect hint or suggestion.
Example
She gave no intimation of her plans.
C1 noun /ˈɪmɪnəns/

imminence

Meaning
the state of being about to happen
Example
The imminence of the storm forced people to take shelter.
C1 adjective /ˌɪnɔːrˈɡænɪk/

inorganic

Meaning
relating to substances that are not derived from living organisms; lacking organic structure or growth
Example
Inorganic compounds are commonly studied in chemistry labs.
C1 adjective /ɪnˈfɜːm/

infirm

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

interstellar

Meaning
Occurring or situated between stars.
Example
Scientists study interstellar travel possibilities.
C1 adjective /ɪˈledʒ.ə.bəl/

illegible

Meaning
Not clear enough to be read; unreadable.
Example
The doctor’s handwriting was almost illegible.
C1 adjective /ˌɪnkənˈkluːsɪv/

inconclusive

Meaning
Not leading to a definite result or decision.
Example
The investigation remained inconclusive due to a lack of evidence.
C1 verb /ɪmˈpɑːrt/

impart

Meaning
to make information known; to bestow or communicate
Example
The teacher imparted valuable knowledge to her students.
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.
C1 noun /ˌɪmpɔːrˈteɪʃən/

importation

Meaning
The act of bringing goods or services into a country from abroad
Example
The importation of luxury goods is strictly regulated.