| Term | Definition |
| inchoate | recently begun |
| incidence | rate of occurence; particular occurence |
| incidental | not essential; minor |
| incipient | beginning |
| incisive | cutting |
| incite | arouse to action |
| inclement | stormy; unkind |
| incline | slope |
| inclined | tending or leaning toward;bent |
| inclusive | tending to include all |
| incoherence | unintelligibility; lack of logic |
| incompatible | inharmonious |
| incongruous | not fitting |
| inconsequential | insignificant |
| inconsistency | state of being self-contradictory |
| incontinent | lacking self-restraint |
| incontrovertible | indisputable |
| incorporate | introduce something into a larger whole |
| incorporeal | lacking a material body |
| incorrigible | not correctable |
| incredulous | withholding belief; skeptical |
| increment | increase |
| incriminate | accuse |
| incrustation | hard coating or crust |
| incubate | hatch; scheme |
| inculcate | teach |
| incumbent | obligatory |
| incur | bring upon oneself |
| incursion | temporary invasion |
| indefatigable | tireless |
| indelible | not able to be erased |
| indentation | notch; deep recess |
| indenture | bind as servant or apprentic to master |
| indeterminate | uncertain |
| indicative | suggestive; implying |
| indices | signs; indications |
| indict | charge |
| indifferent | unmoved or unconcerned by |
| indigenous | native |
| indigent | poor |
| indignation | anger at an injustice |
| indignity | offensive or insulting treatment |
| indiscretion | lack of tactfulness or sound judgement |
| indiscriminate | choosing at random |
| indisputable | too certain to be disputed |
| indissoluble | permanent |
| indoctrinate | instruct in a doctrine |
| indolent | lazy |
| indomitable | unconquerable |
| indubitable | unable to be doubted |
| induce | persuade; bring about |
| indulgent | humoring; lenient |
| industrious | diligent |
| inebriated | habitually intoxicated |
| ineffable | cannot be expressed in speech |
| ineffectual | not effective; weak |
| inefficacious | not effective; unable to produce a desired result |
| inept | lacking skill |
| inequity | unfairness |
| inert | inactive |
| inevitable | unavoidable |
| inexorable | relentless |
| infallible | unerring |
| infamous | notoriously bad |
| infantile | childish |
| infer | deduce |
| infernal | pertaining to hell |
| infidel | unbeliever |
| infiltrate | pass into |
| infinitesimal | exceedingly small |
| infirmity | weakness |
| inflated | exaggerated |
| influx | flowing into |
| informal | absence of ceremony |
| infraction | violation |
| infuriate | enrage |
| infusion | act of introducing or instilling a quality |
| ingenious | clever |