An Etymological Dictionary of the German Language/Laus
Laus, f., ‘louse,’ from the equiv. MidHG., MidLG., and OHG. lûs, f.; corresponding to AS. lûs, E. louse, Scand. lús (plur. lýss), Du. luis, ‘louse.’ The word is common to Teut., occurring evelywhere in the same sense. The usual derivation of Laus from the stem of verlieren, Ver-lus-t, lose, löse (root lus), although supported by the analogy of Gr. φθείρ, ‘louse,’ from φθείρω, is dubious, since MidHG. verliesen (prop. ‘to lose’) does not occur at an early period in the sense of ‘to spoil.’ Neither is the derivation from the Teut. root lū̆t, ‘to hide oneself’ (OHG. lûȥȥên, see lauschen), certain.