/ Dictionary / Index U underlayment: Meaning and Definition of Find definitions for: un•der•lay•ment Pronunciation: (un"dur-lā'munt), [key] — n. material laid between a subfloor and a finish floor of linoleum, asphalt tile, etc. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: underlayment (Thesaurus) underlayer underlet Related Content Daily Word Quiz: eureka Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language