"cold-sore," 1540s, from chill (n.) + blain "inflamed swelling or sore on skin." Related: Chilblains.
Entries linking to chilblain
chill n.
Old English ciele, cele "cold, coolness, chill, frost, sensation of suffering from cold, sensation of cold experienced in illness," from Proto-Germanic *kal- "to be cold," from PIE root *gel- "cold; to freeze." In modern use perhaps a back-formation from the verb. Figurative sense "depressing situation or influence" is from 1821 (in Middle English the figurative sense was "suffering, misfortune").
blain n.
Old English blegen "a sore, blister, pustule, inflammatory swelling on the body," from Proto-Germanic *blajinon "a swelling" (source also of Danish blegn, Dutch blein), from PIE *bhlei- "to swell," from root *bhel- (2) "to blow, swell."