lassie (n.)

"young woman, girl," c. 1300, probably from a Scandinavian source akin to Old Swedish løsk kona "unmarried woman" [OED], but other sources say perhaps related to Old Norse löskr "idle, weak," West Frisian lask "light, thin." Liberman suggests Old Danish las "rag," and adds, "Slang words for 'rag' sometimes acquire the jocular meaning 'child' and especially 'girl.'" "Used now only of mean girls" [Johnson, who has an entry for Shakespeare's lass-lorn "forsaken by his mistress"]. Paired with lad since early 15c.

alternative spelling of -y; now mostly of -y (3), but formerly of the others as well.