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ichthyosaurs n. A fossil reptile.
icily adv. Frigidly.
iconoclast n. An image-breaker.
idiom n. A use of words peculiar to a particular language.
idiosyncrasy n. A mental quality or habit peculiar to an individual.
ignominious adj. Shameful.
illusive adj. Deceptive.
illusory adj. Deceiving or tending to deceive, as by false appearance.
imbibe v. To drink or take in.
imbroglio n. A misunderstanding attended by ill feeling, perplexity, or strife.
imbrue v. To wet or moisten.
immaculate adj. Without spot or blemish.
imminence n. Impending evil or danger.
imminent adj. Dangerous and close at hand.
immiscible adj. Separating, as oil and water..
immutable adj. Unchangeable.
impalpable adj. Imperceptible to the touch.
impeccable adj. Blameless.
impecunious adj. Having no money.
impend v. To be imminent.
imperative adj. Obligatory.
imperceptible adj. Indiscernible.
imperious adj. Insisting on obedience.
impertinence n. Rudeness.
imperturbable adj. Calm.
impervious adj. Impenetrable.
impetuosity n. Rashness.
impetuous adj. Impulsive.
impetus n. Any impulse or incentive.
impiety n. Irreverence toward God.
impious adj. Characterized by irreverence or irreligion.
implausible adj. Not plausible.
implicate v. To show or prove to be involved in or concerned
impolitic adj. Inexpedient.
importation n. The act or practice of bringing from one country into another.
importunate adj. Urgent in character, request, or demand.
importune v. To harass with persistent demands or entreaties.
impotent adj. Destitute of or lacking in power, physical, moral, or intellectual.
impracticable adj. Not feasible.
impregnable adj. That can not be taken by assault.
impromptu n. Anything done or said on the impulse of the moment.
impropriety n. The state or quality of being unfit, unseemly, or inappropriate.
improvident adj. Lacking foresight or thrift.
improvise v. To do anything extemporaneously or offhand.
impugn v. To assail with arguments, insinuations, or accusations.
impulsion n. Impetus.
impulsive adj. Unpremeditated.
impunity n. Freedom from punishment.
impute v. To attribute.
inadvertent adj. Accidental.
inarticulate adj. Speechless.
incandescence n. The state of being white or glowing with heat.
incandescent adj. White or glowing with heat.
incapacitate v. To deprive of power, capacity, competency, or qualification.
incarcerate v. To imprison.
incendiary n. Chemical or person who starts a fire-literally or figuratively.
inception n. The beginning.
incessant adj. Unceasing.
inchmeal adv. Piecemeal.
inchoate adj. Incipient.
inchoative n. That which begins, or expresses beginning.
incipience n. Beginning.
incipient adj. Initial.
incisor n. A front or cutting tooth.
incite v. To rouse to a particular action.
incoherence n. Want of connection, or agreement, as of parts or ideas in thought, speech, etc.
inconceivable adj. Incomprehensible.
incongruous adj. Unsuitable for the time, place, or occasion.
inconsistent adj. Contradictory.
indelible adj. That can not be blotted out, effaced, destroyed, or removed.
indicant adj. That which points out.
indicator n. One who or that which points out.
indigence n. Poverty.
indigent adj. Poor.
indignant adj. Having such anger and scorn as is aroused by meanness or wickedness.
indiscernible adj. Not perceptible.
indiscriminate adj. Promiscuous.
indispensable adj. Necessary or requisite for the purpose.
indolence n. Laziness.
induct v. To bring in.
indulgence n. The yielding to inclination, passion, desire, or propensity in oneself or another.
inebriate v. To intoxicate.
ineffable adj. Unutterable.
inept adj. Not fit or suitable.
inert adj. Inanimate.
inestimable adj. Above price.
inevitable adj. Unavoidable.
inexorable adj. Unrelenting.
inexpedient adj. Unadvisable.
inexplicable adj. Such as can not be made plain.
infallible adj. Exempt from error of judgment, as in opinion or statement.
infirm adj. Lacking in bodily or mental strength.
infirmity n. A physical, mental, or moral weakness or flaw.
influx n. Infusion.
infringe v. To trespass upon.
ingenious adj. Evincing skill, originality, or cleverness, as in contrivance or arrangement.
ingenuity n. Cleverness in contriving, combining, or originating.
ingenuous adj. Candid, frank, or open in character or quality.
ingraft v. To set or implant deeply and firmly.
ingratiate v. To win confidence or good graces for oneself.
inherence n. The state of being permanently existing in something.
inherent adj. Intrinsic.
inhume v. To place in the earth, as a dead body.
inimical adj. Adverse.
iniquity n. Gross wrong or injustice.
injunction n. Mandate.
inkling n. A hint.
inland adj. Remote from the sea.
inmost adj. Deepest within.
innocuous adj. Harmless.
innovate v. To introduce or strive to introduce new things.
innuendo n. Insinuation.
innumerable adj. Countless.
inopportune adj. Unsuitable or inconvenient, especially as to time.
inquisition n. A court or tribunal for examination and punishment of heretics.
inquisitive adj. Given to questioning, especially out of curiosity.
inquisitor n. One who makes an investigation.
inroad n. Forcible encroachment or trespass.
insatiable adj. That desires or craves immoderately or unappeasably.
inscrutable adj. Impenetrably mysterious or profound.
insensible adj. Imperceptible.
insentient adj. Lacking the power of feeling or perceiving.
insidious adj. Working ill by slow and stealthy means.
insight n. Intellectual discernment.
insinuate v. To imply.
insipid adj. Tasteless.
instantaneous adj. Done without perceptible lapse of time.
instigate v. To provoke.
instigator n. One who incites to evil.
instill v. To infuse.
instructive adj. Conveying knowledge.
insufficiency n. Inadequacy.
insular adj. Pertaining to an island.
insulate v. To place in a detached state or situation.
insuperable adj. Invincible.
insuppressible adj. Incapable of being concealed.
insurgence n. Uprising.
insurgent n. One who takes part in forcible opposition to the constituted authorities of a place.
insurrection n. The state of being in active resistance to authority.
intangible adj. Not perceptible to the touch.
integrity n. Uprightness of character and soundness of moral principle.
intemperance n. Immoderate action or indulgence, as of the appetites.
intension n. The act of stringing or stretching, or state of being strained.
intention n. That upon which the mind is set.
interact v. To act reciprocally.
intercede v. To mediate between persons.
intercept v. To interrupt the course of.
intercession n. Entreaty in behalf of others.
intercessor n. A mediator.
interdict n. Authoritative act of prohibition.
interim n. Time between acts or periods.
interlocutor n. One who takes part in a conversation or oral discussion.
intermediate adj. Being in a middle place or degree or between extremes.
interminable adj. Having no limit or end.
intermit v. To cause to cease temporarily.
intermittent adj. A temporary discontinuance.
interpolation n. Verbal interference.
interpose v. To come between other things or persons.
interrogate v. To examine formally by questioning.
interrogative adj. Having the nature or form of a question.
interrogatory n. A question or inquiry.
intervale n. A low tract of land between hills, especially along a river.
intestacy n. The condition resulting from one's dying not having made a valid will.
intestate adj. Not having made a valid will.
intracellular adj. Occurring or situated within a cell.
intramural adj. Situated within the walls of a city.
intricacy n. Perplexity.
intricate adj. Difficult to follow or understand.
intrinsic adj. Inherent.
introductory adj. Preliminary.
introgression n. Entrance.
intromit v. To insert.
introspection n. The act of observing and analyzing one's own thoughts and feelings.
introversion n. The act of turning or directing inward, physically or mentally.
inundate v. To fill with an overflowing abundance.
inundation n. Flood.
inure v. To harden or toughen by use, exercise, or exposure.
invariable adj. Unchangeable.
invective n. An utterance intended to cast censure, or reproach.
inveigh v. To utter vehement censure or invective.
inventive adj. Quick at contrivance.
inverse adj. Contrary in tendency or direction.
inversion n. Change of order so that the first shall become last and the last first.
investor n. One who invests money.
inveterate adj. Habitual.
invidious adj. Showing or feeling envy.
invoke v. To call on for assistance or protection.
involution n. Complication.
inwardly adv. With no outward manifestation.
iota n. A small or insignificant mark or part.
irascible adj. Prone to anger.
irate adj. Moved to anger.
ire n. Wrath.
iridescence n. A many-colored appearance.
iridescent adj. Exhibiting changing rainbow-colors due to the interference of the light.
irradiance n. Luster.
irradiate v. To render clear and intelligible.
irrefragable adj. That can not be refuted or disproved.
irrefrangible adj. That can not be broken or violated.
irrepressible adj. That can not be restrained or kept down.
irreverence n. The quality showing or expressing a deficiency of veneration, especially for sacred things.
irreverent adj. Showing or expressing a deficiency of veneration, especially for sacred things.
irreverential adj. Showing or expressing a deficiency of veneration, especially for sacred things.
irrigant adj. Serving to water lands by artificial means.
irrigate v. To water, as land, by ditches or other artificial means.
irritancy n. The quality of producing vexation.
irritant n. A mechanical, chemical, or pathological agent of inflammation, pain, or tension.
irruption n. Sudden invasion.
islet n. A little island.
isochronous adj. Relating to or denoting equal intervals of time.
itinerant adj. Wandering.
itinerary n. A detailed account or diary of a journey.
itinerate v. To wander from place to place.