louse Look up louse at Dictionary.com
O.E. lus, "parasitic insect infecting human hair and skin," from P.Gmc. *lus (cf. O.N., M.Du., O.H.G. lus, Ger. Laur). Slang meaning "obnoxious person" is from 1630s. The plural lice (O.E. lys) shows effects of i-mutation. The verb meaning "to clear of lice" is from mid-15c.; to louse up "ruin, botch" first attested 1934.