| Term | Definition |
| incongruous | unsuitable for the time, place, or occasion; inappropriate, incompatible |
| indelible | cannot be erased or destroyed |
| indigenous | native to a place |
| indolent | habitually inactive or idle; lazy; disinclined to work or exertion |
| indomitable | unconquerable, can't be dominated |
| ineffable | unutterable, indescribable, inexpressible |
| ineluctable | certain; inevitable; impossible to avoid or evade:"inescapable conclusion" |
| inexorable | unrelenting, inflexible, unyielding, relentless |
| ingenuous | candid, frank, open in character; lacking in cunning, guile, worldliness; artless |
| innocuous | harmless, not likely to offend or provoke |
| inscrutable | impenetrably mysterious or profound; difficult to fathom or understand |
| insipid | tasteless, dull, boring |
| insouciant | nonchalant, carefree, blithely unconcerned |
| intransigent | not capable of being swayed or diverted from a course; uncompromising; refusing to be reconciled |
| intrepid | fearless, bold |
| inveterate | habitual, long established; deep-rooted |
| invincible | cannot be conquered, subdued; unconquerable |
| inviolable | safe from violation or assault; invincible |
| irascible | prone to anger; irritable |
| irksome | tedious; causing annoyance, weariness or vexation |
| itinerant | wandering |
| insolent | rude, impertinent; marked by casual disrespect; impudent |
| indefatigable | never tired, tireless |
| inept | clumsy, awkward; incapable, foolish, nonsensical |
| inevitable | certain, unavoidable |