From Proto-Italic *skelos, from Proto-Indo-European *skelos (“curve, bending”), from *(s)kel- (“to curve, bend”). This etymology presupposes a semantic shift from "crooked" to "wicked, bad". Cognate with Proto-Germanic *skelhaz (whence Dutch scheel, German scheel), Ancient Greek σκέλος (skélos), σκολιός (skoliós).