| Term | Definition |
| ignoble | Lacking or having low moral standards; not noble in character |
| imbibe | To take into the mind; absorb |
| impassive | Devoid of any signs of emotion; expressionless |
| imperious | Commanding, demanding; urgent |
| ingratiate | To gain favor deliberately as so to gain oneself an advantage |
| inherent | Relating to the essential character of something; built-in |
| insensate | Lacking sensibility or depth of understanding; naive, foolish |
| insolent | Insultingly arrogant; overbearing |
| insular | Characteristic of an isolated, remote people, esp. with a narrow viewpoint |
| insuperable | Incapable of being overcome or defeated |
| inter | To bury |
| interlocutor | One who participates in discussion |
| internecine | Mutually destructive; equally devastating to both sides |
| interregnum | A temporary halt of the typical operations of government or control |
| intimation | A subtle, indirect hint |
| intractable | Not easily manipulated or managed |
| intransigent | Uncompromising; unyielding; refusing to abandon an extreme position |
| intrepid | Fearless; extremely brave |
| inundate | To cover with a flood; to overwhelm with a flood |
| inveterate | Firmly established, esp. with respect to a habit or attitude |
| irascible | Easily agitated or angered; hot-tempered |
| ironic | Contrary or opposite of what was expected |
| irreverent | Disrespectful in a gentle or humorous way |
| itinerant | Wandering from place to place (like a nomad); unsettled |