/ Dictionary / Index L long-acting: Meaning and Definition of Find definitions for: long-act•ing Pronunciation: (lông'ak'ting, long'-), [key] — adj. Pharm. sustained-release. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: long-acting (Thesaurus) long account long-ago Related Content Daily Word Quiz: arboreal Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language