| Term | Definition |
| Imperious | (adj.) commanding, domineering |
| Impertinent | (adj.) rude, insolent |
| Impervious | (adj.) impenetrable, incapable of being affected |
| Impetuous | (adj.) rash; hastily done |
| Impinge | to impact, affect, make an impression |
| Impinge | to encroach, infringe |
| Implacable | incapable of being appeased or mitigated |
| Impudent | (adj.) casually rude, insolent, impertinent |
| Inchoate | (adj.) unformed or formless, in a beginning stage |
| Incontrovertible | (adj.) indisputable |
| Indefatigable | (adj.) incapable of defeat, failure, decay |