late Old English heorcnian "to give ear, listen" (intransitive); hear with attention" (transitive), a suffixed form of *heorcian (root of hark); from Proto-Germanic *hausjan (see hear). Harken is the usual spelling in U.S. and probably is better justified by etymology; OED says preference for hearken in British use likely is from influence of hear.[hearken etymology, hearken origin, 英语词源]