serpentine (n.)

c. 1400, "plant reputed to contain antivenom," from Old French serpentin name of a precious stone, noun use of adjective meaning "of a snake, snake-like; sly, deceptive," from Late Latin serpentius "of a serpent," from Latin serpentem (nominative serpens) "snake" (see serpent). As the name of a greenish igneous rock consisting mainly of hydrous magnesium silicate, attested from early 15c.

"twisting, winding," 1610s; see serpent + -ine (1). An earlier adjective meaning "having the evil qualities of a serpent" is recorded from late 14c., from the French source of serpentine (n.). The winding lake of that name in Hyde Park, London, was constructed in 1730.