c.1300, from a Scandinavian source, probably akin to O.Swed. løsk kona "unmarried woman," but also perhaps related to O.N. loskr "idle, weak," W.Fris. lask "light, thin." "Used now only of mean girls" [Johnson, who also has lasslorn "forsaken by his mistress"]. Scottish dim. lassie first recorded 1725.