| Term | Definition |
| improvisation | act of improvising, or something that has been improvised |
| impudence | act or condition of being impudent |
| impugn | question |
| inaccessible | unreachable |
| inane | silly |
| inappropriate | unsuitable |
| incalculable | countless |
| incandescent | glowing |
| incantation | chant |
| incapacitate | weaken |
| incarnate | personified |
| incarnation | personification |
| incendiary | rousing |
| incense | infuriate |
| incessant | continuous |
| incidence | occurrence |
| incidental | secondary |
| incisive | insightful |
| incite | rouse |
| inclination | liking |
| inclined | minded |
| incompetent | useless |
| incomprehensible | impossible to understand |
| incongruent | different |
| incongruous | out-of-place |
| incontrovertible | undeniable |
| incorporate | combine |
| incorrigible | habitual |
| incredulous | doubtful |
| inculcate | teach |
| indecorous | rude |
| indefatigable | tireless |
| indict | charge |
| indictment | charge |
| indifferent | uninterested |
| indigenous | native |
| indigent | poor |
| indignant | irate |
| indiscriminate | undiscriminating |
| indispensable | vital |
| indistinct | unclear |
| indolence | idleness |
| indolent | idle |
| indomitable | unconquerable |
| indubitable | doubtless |
| induce | persuade |
| indulgence | treat |
| indulgent | showing or inclined to show indulgence |
| industrious | diligent |
| inebriate | intoxicate |
| ineffable | inexpressable |
| inefficacious | useless |
| ineluctable | inevitable |
| inept | clumsy |
| inertia | inactivity |
| inevitable | certain |
| inexorable | relentless |
| inexplicable | unexplainable |