/ Dictionary / Index A arc second: Meaning and Definition of Find definitions for: arc' sec"ond Pronunciation: [key] second (def. 4). Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: arcsecond (Thesaurus) arc secant arc sin Related Content Daily Word Quiz: exemplary Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language