| inestimable | too great to calculate or estimate; immeasurable | |
| ineluctable | impossible to avoid or evade; inevitable | |
| ineffable | Too great or extreme to be expressed or described in words | |
| industrious | Diligent and hard-working | |
| indomitable | Impossible to subdue or defeat | |
| indigenous | Originating or occurring naturally in a particular place; native | |
| indictment | A formal charge or accusation of a serious crime | |
| indefatigable | Incapable of being tired out; not yielding to fatigue; untiring. | |
| incumbent | Noun: a person who currently holds a particular position or office | |
| inculcate | To instill (an attitude, idea, or habit) by persistent instruction | |