Hearken, v. i. [imp. & p. p. Hearkened; p. pr. & vb. n. Hearkening.]
Etymology: [OE. hercnen, hercnien, AS. hercnian, heorcnian, fr. hiéran, h, to hear; akin to OD. harcken, horcken, LG. harken, horken, G. horchen. See Hear, and cf. Hark..]
1. To listen; to lend the ear; to attend to what is uttered; to give heed; to hear, in order to obey or comply. The Furies hearken, and their snakes uncurl. Dryden. Hearken, O Israel, unto the statutes and unto the judgments, which I teach you. Deut. iv. 1.
2. To inquire; to seek information. [Obs.] "Hearken after their offense." Shak.
Syn. -- To attend; listen; hear; heed. See Attend, v. i.
1 other Webster entry under this spelling
Hearken, v. t.
1. To hear by listening. [Archaic] [She] hearkened now and then Some little whispering and soft groaning sound. Spenser.
2. To give heed to; to hear attentively. [Archaic] The King of Naples . . . hearkens my brother's suit. Shak. To hearken out, to search out. [Obs.] If you find none, you must hearken out a vein and buy. B. Johnson.
Shades of meaning
Fernald lists hearken only as an antonym, under call.
He lists it without comment; the entries above explain its neighbors.