Hark, v. i.
Etymology: [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.
Shades of meaning
Fernald has no entry of its own for hark; he lists it under listen.
He lists it without comment; the entries above explain its neighbors.