/ Dictionary / Index A arcus: Meaning and Definition of Find definitions for: ar•cus Pronunciation: (är'kus), [key] — pl. -cus. a dense, horizontal, roll-shaped cloud sometimes occurring at the lower front portion of a cumulonimbus. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: arcus (Thesaurus) arcuation arcus senilis Related Content Daily Word Quiz: lyre Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language