c. 1300, ranclen, of a sore, wound, etc., "to fester," from Old French rancler, earlier raoncler, draoncler "to suppurate, run," from draoncle "abscess, festering sore," from Medieval Latin dracunculus, literally "little dragon," diminutive of Latin draco "serpent, dragon" (see dragon). According to OED (citing Skeat and also Godefroy's "Dictionnaire De L'ancienne Langue Française"), the notion is of an ulcer caused by a snake's bite. Transitive meaning "cause to fester" is from c. 1400. Figurative use, of feelings, etc., is from 16c. Related: Rankled; rankling.