dace (n.)

type of small European freshwater fish, mid-15c., also dars, dase, dare, from Old French darz"a dace," nominative or plural of dart "dart" (see dart (n.)). So called for its swiftness. Another theory traces it to a Medieval Latin darsus "a dart," which is said to be of Gaulish origin. Also used of similar or related fish. For loss of -r- before -s-, compare bass (n.1) from barse and see ass (n.2).