Source : Webster's Revised Unabridged Dictionary (1913)

Lass \Lass\, n. [OE. lasse; prob. of Celtic origin; cf. W.
   llodes girl, fem. of llawd lad. (?). See {Lad} a youth.]
   A youth woman; a girl; a sweetheart.

Source : WordNet®

lass
     n : a girl or young woman who is unmarried [syn: {lassie}, {young
         girl}, {jeune fille}]