An Etymological Dictionary of the German Language/lasch
lasch, adj., ‘slack,’ from MidHG. and OHG. *lasc; comp. OIc. lǫskr (Goth. *lasqs-), adj., ‘slack, weary’; formed with a suffix sk from the root laß, lassen (Goth. *lasqa- would represent *latsqa-). Yet it is not improbable, since lasch is first recorded in ModHG., that the root was borrowed from a Rom. class similar in sound (comp. Fr. lâche, Ital. lasco,‘idle’).