| incoherent | Not able to be understood; nonsensical. | |
| incipient | In an initial stage; beginning to happen or develop | |
| inchoate | just begun and so not fully formed or developed; rudimentary | |
| incensed | Very angry; enraged | |
| incandescent | Emitting light as a result of being heated | |
| inane | Lacking sense or meaning; silly | |
| inalienable | Not subject to being taken away from or given away by the possessor | |
| impugn | To dispute the truth, validity, or honesty of a statement or motive; call into question | |
| impudence | The quality of being impudent; not showing due respect for another person | |
| impromptu | Done without being planned, organized, or rehearsed | |