| Term | Definition |
| inveterate | deep-rooted; habitual |
| invidious | designed to create ill will or envy |
| invincible | unconquerable |
| inviolable | secure from corruption, attack or violation; unassailable |
| invocation | prayer for help; calling upon as a reference or support |
| invoke | call upon; ask for |
| invulnerable | incapable of injury |
| iota | very small quantity |
| irascible | irritable; easily angered |
| irate | angry |
| iridescent | exhibiting rainbowlike colors |
| irksome | annoying; tedious |
| ironic | occurring in an unexpected and contrary manner |
| irony | hidden sarcasm or satire; use of words that seem to mean the opposite of what they actually mean |
| irreconcilable | incompatible; not able to be resolved |
| irrefutable | indisputable; incontrovertible; undeniable |
| irrelevant | not applicable; unrelated |
| irremediable | incurable; uncorrectable |
| irreparable | not able to be corrected or repaired |
| irrepressible | unable to be restrained or held back |
| irreproachable | blameless; impeccable |
| irresolute | uncertain how to act; weak |
| irretrievable | impossible to recover or regain; irreparable |
| irreverence | lack of proper respect |
| irrevocable | unalterable; irreversible |
| isotope | varying form of an element |
| isthmus | narrow neck of land connecting two larger bodies of land |
| itinerant | wondering; traveling |
| itinerary | plan of a trip |
| jabber | chatter rapidly or unintelligibly |
| jaded | to become tired of something; fatigued; surfeited |
| jargon | language used by a special group; technical terminology; gibberish |
| jaundiced | prejudiced ( envious; hostile or resentful); yellowed |
| jaunt | trip; short journey |
| jaunty | lighthearted; animated; easy and carefree |
| jeopardize | endanger; imperil; put at risk |
| jettison | throw overboard |
| jibe | agree; be in harmony |
| jingoist | extremely aggressive and militant patriot; warlike chauvinst |
| jocose | given to joking |
| jocular | said or done in jest (playfully) |
| jocund | merry |
| jollity | gaiety; cheerfulness; feeling jolly and jovial and full of good humor |
| jostle | shove; bump |
| jovial | good natured; merry |
| jubilation | rejoicing |
| judicious | sound in judgment; wise |
| juggernaut | irresistible crushing force |
| juncture | crisis; joining point |
| junket | trip; especially one taken for pleasure by an official at public expense |
| junta | group of person joined in political intrigue (plot) |
| jurisprudence | science of law |
| justification | good or just reason; defense; excuse |
| juxtapose | place side by side |
| kaleidoscope | tube in which patterns made by the reflection in mirrors of colored pieces of glass, etc., produce interesting symmetrical effects |
| ken | range of knowledge |
| kernel | central or vital part; whole seed( as of corn) |
| killjoy | One who spoils the enthusiasm or fun of others ;grouch; spoilsport |
| kindle | start a fire; inspire |
| kindred | related; similar in nature or character |
| kinetic | producing motion |
| kismet | fate |
| kleptomaniac | person who has a compulsive desire to steal |
| knave | untrustworthy person; rogue; scoundrel |
| knead | mix; work dough |
| knell | tolling of a ,, especially to indicate a funeral, disaster, etc.; sound of a funeral bell |
| knit | contract into wrinkles; grow together |
| knoll | little round hill |
| knotty | intricate; difficult; tangled |
| kudos | honor; glory; praise |
| labile | likely to change; unstable |
| laborious | demanding much work or care; tedious |
| labyrinth | maze; An intricate structure of interconnecting passages through which it is difficult to find one's way; |
| laceration | torn; ragged wound |
| lachrymose | producing tear |
| lackadaisical | lacking purpose or zest; halfhearted; languid |
| lackluster | dull |
| laconic | brief and to the point |
| laggard | slow; sluggish |