| Words | Synonyms | Antonyms |
| Ideal | exemplary, model, standard, perfect, supreme, hypothetical | flawed, imperfect, problematic |
| Identical | same, similar, equal, equivalent, tantamount, even | distinct, diverse, dissimilar |
| Ignite | kindle, fire, light, inflame, alight, burn, incense | extinguish, pacify, quench |
| Ignorant | illiterate, uneducated, unaware, oblivious, unacquainted, benighted | aware, knowledgeable, literate |
| Illegitimate | illegal, illicit, outlawed, bastard, spurious, misbegotten | authorized, ethical, moral |
| Illicit | lawless, unlawful, wrongful, felonious, clandestine, adulterous | legitimate, noble, proper |
| Immense | enormous, monumental, vast, titanic, colossal, elephantine | tiny, minute, paltry |
| Impartial | dispassionate, equitable, indifferent, unbiased, nonpartisan, just | prejudiced, partial, discriminating |
| Impromptu | extemporary, improvised, offhand, unrehearsed, ad-lib, unprepared | deliberate, planned, premeditated |
| Inclusive | comprehensive, expansive, extensive, sweeping, widespread, extended | exclusive, narrow, selective |
| Increment | advance, boost, hike, increase, jump, raise | decrease, loss, slump |
| Indifferent | dispassionate, objective, just, apathetic, nonpartisan, square | concerned, caring, sympathetic |
| Industrious | assiduous, objective, just, apathetic, nonpartisan, square | concerned, caring, sympathetic |
| Inevitable | certain, inescapable, unavoidable, definite, sure, doomed | uncertain, unlikely, unsure |
| Infinite | boundless, eternal, endless, unlimited, countless, innumerable | definite, limited, measurable |
| Initial | inceptive, beginning, introductory, primary, primordial | closing, final, last |
| Innovative | ingenious, inventive, original, improvised, unprecedented, novel | customary, habitual, traditional |
| Inquisitive | curious, nosy, snoopy, inquiring, questioning, investigate | disinterested, indifferent, incurious |
| Insane | crazy, daft, unsound, maniac, lunatic, dotty | sane, rational, logical |
| Insignificant | trivial, inconsequent, inconsiderable, meager, immaterial, negligible | significant, substantial, valuable |
| Intensify | aggravate, deepen, enhance, heighten, redouble, increase | weaken, soothe, lower |
| Intervene | interfere, intrude, meddle, obtrude, intercede, interpose | ignore, withdraw, avoid |
| Intimate | close, familiar, friendly, interior, confidential, personal | formal, incompatible, cool |
| Invert | reverse, transpose, turn, flip, upturn, backtrack | advance, forward, hold |
| Invincible | impregnable, indomitable, unconquerable, unbeatable, unyielding, insurmountable | beatable, conquerable, breakable |
| Irritate | aggravate, bug, exasperate, fret, peeve, nettle | assuage, please, aid |
| Isolate | seclude, segregate, insulate, separate, detach, remove | integrate, incorporate, mingle |
| Itinerant | nomadic, vagabond, vagrant, migratory, migrant, wanderer | permanent, settled, resident |
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