Etymology

From Middle English chelidre, chelyder, chelydre, from Old French chelidre, chelydre, from Latin chelȳdrus ‎(“fetid water serpent”), from Ancient Greek χέλυδρος ‎(khéludros, “amphibious serpent”), from χέλυς ‎(khélus, “tortoise”) + ὕδρος ‎(húdros, “water serpent”). Cognate of French chélydre.