An Etymological Dictionary of the German Language/schal

by Friedrich Kluge

schal, adj., ‘hollow, stale, flat,’ from MidHG. (rare) schal, adj., ‘turbid,’ to which MidHG. verschaln and schaln, ‘to become dim’; comp. Du. verschalen, ‘to get flat or stale,’ E. shallow. The term, the origin of which is obscure, is wanting in the UpG. dials.