Do you know ghouls from goblins and ghosts?
late 12c., from Old English *heorcian, perhaps an intensive form from base of hieran (see hear). Cf. talk/tale. Cognate with Old Frisian harkia "listen," Middle Dutch horken, Old High German horechon, German horchen. To hark back (1829) originally referred to hounds returning along a track when the scent has been lost, till they find it again. Related: Harked; harking.