Skulk comes from Middle English skulken, of Scandinavian origin, akin to Norwegian skulka ('to lurk') and Danish skulke ('to shirk, play truant'). The historical chain includes Old Norse skulka. The quoted older senses, "to lurk" and "to shirk, play truant", supply the semantic anchors for skulk. The formation is best read as borrowed: the word skulk carries its older form-history into a compact English lexical shape. In present English it is used as a verb, "to move or lurk furtively in order to avoid notice". English derivatives include skulker; related English forms include skulking. The result is a verb whose etymology preserves both the older form and the later English specialization.