Source : Webster's Revised Unabridged Dictionary (1913)

Hark \Hark\, v. i. [OE. herken. See {Hearken}.]
   To listen; to hearken. [Now rare, except in the imperative
   form used as an interjection, Hark! listen.] --Hudibras.

   {Hark away!} {Hark back!} {Hark forward!} (Sporting), cries
      used to incite and guide hounds in hunting.

   {To hark back}, to go back for a fresh start, as when one has
      wandered from his direct course, or made a digression.

            He must have overshot the mark, and must hark back.
            Haggard. He harked back to the subject. --W. E.
                                                  Norris.

Source : WordNet®

hark back
     v : go back to something earlier; "This harks back to a previous
         remark of his" [syn: {return}, {come back}, {recall}]