"go or move furtively; withdrawn into a close, secure place for concealment," c. 1300 (late 13c. as a surname), skulken, from a Scandinavian source such as Norwegian skulke "to shirk, malinger," Danish skulke "to spare oneself, shirk," Swedish skolka "to shirk, skulk, slink, play truant."
Common in Middle English but lacking in 15c.-16c. writing; it was possibly re-elevated 17c. Related: Skulked; skulking; skulkery. Skulker as an old name for the hare, also for the devil, is attested from c. 1300. Middle English also had skulkerie "concealment, stealthy behavior or action" c. 1400.