/ Dictionary / Index M millisecond: Meaning and Definition of Find definitions for: mil•li•sec•ond Pronunciation: (mil'u-sek"und), [key] — n. one thousandth of a second. Abbr.: msec Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: millisecond (Thesaurus) milliroentgen millivolt Related Content Daily Word Quiz: censure Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language