- intrude: To come in without leave or license.
- intrusion: The act of entering without warrant or invitation; encroachment.
- intuition: Instinctive knowledge or feeling.
- inundate: To fill with an overflowing abundance.
- inundation: Flood.
- inure: To harden or toughen by use, exercise, or exposure.
- invalid: Having no force, weight, or cogency.
- invalid: One who is disabled by illness or injury.
- invalidate: To render of no force or effect.
- invaluable: Exceedingly precious.
- invariable: Unchangeable.
- invasion: Encroachment, as by an act of intrusion or trespass.
- invective: An utterance intended to cast censure, or reproach.
- inveigh: To utter vehement censure or invective.
- inventive: Quick at contrivance.
- inverse: Contrary in tendency or direction.
- inversion: Change of order so that the first shall become last and the last first.
- invert: To turn inside out, upside down, or in opposite direction.
- investigator: One who investigates.
- investor: One who invests money.
- inveterate: Habitual.
- invidious: Showing or feeling envy.
- invigorate: To animate.
- invincible: Not to be conquered, subdued, or overcome.
- inviolable: Incapable of being injured or disturbed.
- invoke: To call on for assistance or protection.
- involuntary: Unwilling.
- involution: Complication.
- involve: To draw into entanglement, literally or figuratively.
- invulnerable: That can not be wounded or hurt.
- inwardly: With no outward manifestation.
- iota: A small or insignificant mark or part.
- irascible: Prone to anger.
- irate: Moved to anger.
- ire: Wrath.
- iridescence: A many-colored appearance.
- iridescent: Exhibiting changing rainbow-colors due to the interference of the light.
- irk: To afflict with pain, vexation, or fatigue.
- irksome: Wearisome.
- irony: Censure or ridicule under cover of praise or compliment.
- irradiance: Luster.
- irradiate: To render clear and intelligible.
- irrational: Not possessed of reasoning powers or understanding.
- irreducible: That can not be lessened.
- irrefragable: That can not be refuted or disproved.
- irrefrangible: That can not be broken or violated.
- irrelevant: Inapplicable.
- irreligious: Indifferent or opposed to religion.
- irreparable: That can not be rectified or made amends for.
- irrepressible: That can not be restrained or kept down.