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: Webster's Revised Unabridged Dictionary (1913)