| Term | Definition |
| insolvent | unable to pay bills; bankrupt |
| intermittent | occurring at intervals; periodic; not constant or continual |
| intractable | stubborn; immovable |
| intrinsic | located within the very nature of an object or person; inherent |
| invert | turn upside down or inside out; reverse position |
| irascible | easily angered |
| irony | an unexpected outcome, or the use of a word that is the opposite of its literal meaning |
| irresolute | indecisive; unsure |
| irreverent | disrespectful |
| jargon | specialized language used by a particular group |
| jaundice | yellow color; or, envy or resentment |
| jaunty | lively; perky; sprightly |
| jeopardy | the threat or possibility of danger |
| jettison | to throw overboard; to discard |
| jocular | joking; playful; jesting; witty |
| jubilant | filled with joy |
| judicious | wise; making good decisions |
| juncture | point in time, especially a crucial one; joint or connection |
| juxtapose | to place side-by-side |
| kindle | to start a fire; ignite; arouse |
| kinetic | in motion; active |
| laconic | quiet; of few words; terse |
| lament | express sorrow; complain |
| languish | lose energy or motivation; become weak or depressed |
| latent | existing but inactive, such as a certain quality; dormant |
| laud | praise; worship; extol |
| legacy | something inherited, either from an ancestor or from the past itself |
| lethargic | tired; sluggish; drowsy |
| levity | lightness; playfulness; jocularity |
| insolent | rude; haughty |