intrigue n. A plot or scheme, usually complicated and intended to accomplish something by secret ways.
intrinsic adj. Inherent.
introductory adj. Preliminary.
introgression n. Entrance.
intromit v. To insert.
introspect v. To look into.
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.
introvert v. To turn within.
intrude v. To come in without leave or license.
intrusion n. The act of entering without warrant or invitation; encroachment.
intuition n. Instinctive knowledge or feeling.
inundate v. To fill with an overflowing abundance.
inundation n. Flood.
inure v. To harden or toughen by use, exercise, or exposure.
invalid adj. Having no force, weight, or cogency.
invalid n. One who is disabled by illness or injury.
invalidate v. To render of no force or effect.
invaluable adj. Exceedingly precious.
invariable adj. Unchangeable.
invasion n. Encroachment, as by an act of intrusion or trespass.
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.
invert v. To turn inside out, upside down, or in opposite direction.
investigator n. One who investigates.
investor n. One who invests money.
inveterate adj. Habitual.
invidious adj. Showing or feeling envy.
invigorate v. To animate.
invincible adj. Not to be conquered, subdued, or overcome.
inviolable adj. Incapable of being injured or disturbed.
invoke v. To call on for assistance or protection.
involuntary adj. Unwilling.
involution n. Complication.
involve v. To draw into entanglement, literally or figuratively.
invulnerable adj. That can not be wounded or hurt.
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.
irk v. To afflict with pain, vexation, or fatigue.
irksome adj. Wearisome.
irony n. Censure or ridicule under cover of praise or compliment.
irradiance n. Luster.
irradiate v. To render clear and intelligible.
irrational adj. Not possessed of reasoning powers or understanding.
irreducible adj. That can not be lessened.
irrefragable adj. That can not be refuted or disproved.
irrefrangible adj. That can not be broken or violated.
irrelevant adj. Inapplicable.
irreligious adj. Indifferent or opposed to religion.
irreparable adj. That can not be rectified or made amends for.
irrepressible adj. That can not be restrained or kept down.
irresistible adj. That can not be successfully withstood or opposed.
irresponsible adj. Careless of or unable to meet responsibilities.
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.
irreversible adj. Irrevocable.
irrigant adj. Serving to water lands by artificial means.
irrigate v. To water, as land, by ditches or other artificial means.
irritable adj. Showing impatience or ill temper on little provocation.
irritancy n. The quality of producing vexation.
irritant n. A mechanical, chemical, or pathological agent of inflammation, pain, or tension.
irritate v. To excite ill temper or impatience in.
irruption n. Sudden invasion.
isle n. An island.
islet n. A little island.
isobar n. A line joining points at which the barometric pressure is the same at a specified moment.
isochronous adj. Relating to or denoting equal intervals of time.
isolate v. To separate from others of its kind.
isothermal adj. Having or marking equality of temperature.
itinerant adj. Wandering.
itinerary n. A detailed account or diary of a journey.
itinerate v. To wander from place to place.