/ Dictionary / Index U underact: Meaning and Definition of Find definitions for: un•der•act Pronunciation: (un"dur-akt'), [key] — v.t., v.i. to underplay. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: underact (Thesaurus) underachiever underactive Related Content Daily Word Quiz: fabricate Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language