| Term | Definition |
| inchoate | recently begun; rudimentary; elementary |
| incidence | rate of occurrence; particular occurrence |
| incidental | not essential; minor |
| incipient | beginning; in an early stage |
| incisive | cutting; sharp |
| incite | arouse to action; goad; motivate; induce to exist |
| inclement | stormy; unkind |
| incline | slope; slant |
| inclined | tending to be leaning toward; bent |
| inclusive | tending to include all |
| incognito | with identity concealed or disguised |
| incoherent | unintelligible; muddled; illogical |
| incommodious | not spacious; inconvenient |
| incompatible | inharmonious |
| incongruity | lack of harmony; absurdity |
| inconsequential | insignificant; not important |
| inconsistency | state of being self contradictory; lack of uniformity or steadiness |
| incontinent | lacking self restraint; licentious |
| incontrovertible | indisputable; not open to question |
| incorporate | introducing something into a larger whole; combine; unite |
| incorporeal | lacking a material body; insubstantial |
| incorrigible | uncorrectable |
| incredulity | tendency to disbelief |
| incredulous | withholding belief; skeptical |
| increment | increase |
| incriminate | accuse; serve as evidence against |
| incrustation | hard coating or crust |
| incubate | hatch |
| incubus | burden; mental care; nightmare |
| inculcate | teach |
| incumbent | obligatory; currently holding an office |
| incur | bring upon oneself |
| incursion | temporary invasion |
| indefatigable | tireless |
| indelible | not able to be erased |
| indemnify | make secure against loss; compensate for loss |
| indentation | notch; deep recess |
| indenture | bind as servant or apprentice to master |
| indeterminate | uncertain; not clearly fixed |
| indicative | suggestive; implying |
| indices | signs; indications |
| indict | charge |
| indifferent | unmoved or unconcerned by; mediocre |
| indigence | poverty |
| indigenous | native |
| indigent | poor; destitute |
| indignation | anger at an injustice |
| indignity | offensive or insulting treatment |
| indiscriminate | choosing at random; confused |
| indisputable | to certain to be disputed |
| indissoluble | permanent |
| indite | write |
| indolent | lazy |
| indomitable | unconquerable; unyielding |
| indubitable | unable to be doubted; unquestionable |
| induce | persuade; bring about |
| inductive | pertaining to induction or proceeding from the specific to the general |
| indulgent | humoring; yielding; lenient |
| industrious | diligent; hard working |
| inebriated | habitually intoxicated; drunk |
| ineffable | unutterable; cannot be expressed in speech |
| ineffectual | not effective; weak |
| ineluctable | irresistible; not to be escaped |
| inept | lacking skill; unsuited; incompetent |
| inequity | unfairness |
| inerrancy | infallibility; Freedom from error or untruths; exemption from error |
| inert | inactive; lacking power to move |
| inevitable | unavoidable |
| inexorable | relentless; unyielding; implacable |
| infallible | unerring; incapable of error |
| infamous | notoriously bad |
| infantile | childish; infant-like |
| infer | deduce; conclude |
| infernal | pertaining to hell; devilish |
| infidel | unbeliever |
| infiltrate | pass into or through; penetrate ( an organization) sneakily |
| infinitesimal | very small |
| infirmity | weakness |
| inflated | exaggerated; pompous; enlarged ( with air or gas) |
| influx | flowing into |
| infraction | violation ( of a rule or regulation); breach |