/ Dictionary / Index U underweight: Meaning and Definition of Find definitions for: un•der•weight Pronunciation: (adj.un'dur-wāt'n.un'dur-wāt&sec), [key] — adj. weighing less than is usual, required, or proper. —n. deficiency in weight below a standard or requirement. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: underweight (Thesaurus) underwear underwent Related Content Daily Word Quiz: secular Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language