/ Dictionary / Index A ad libitum: Meaning and Definition of Find definitions for: ad lib•i•tum Pronunciation: (ad lib'i-tum Lat. äd lib'i-t&oobrevem&sec), [key] at one's pleasure. not obligatory or indispensable. Abbr.: ad lib. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. ad lib ad litem Related Content Daily Word Quiz: procrastinate Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language