An Etymological Dictionary of the German Language/Annotated/laß
laß, adjective, ‘inactive, idle,’ from Middle High German laȥ (ȥȥ), ‘faint, idle, tardy’ (see letzen); it corresponds to Gothic lats, Old Icelandic latr, Anglo-Saxon lœt, Middle Low German lat, adjective, ‘sluggish, idle, lazy.’ A pre-Teutonic adjective formed by gradation from the stem of lassen, lêt, of which lăt- is the weak form (see schlaff, Old High German slăf, from the root slêp). The close correspondence with Latin lassus may be accounted for historically; lassus is an old participle for *ladtus; lad is the pre-Teutonic root on which Modern High German laß is based; compare lasch, lassen, and letzt. The assumption, however, that High German laß was borrowed from the Romance cognates (Italian lasso, French las, Latin lassus) is inconceivable.