The Collaborative International Dictionary of English v.0.48:

Hearken \Heark"en\, v. t.
   1. To hear by listening. [Archaic]
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            [She] hearkened now and then
            Some little whispering and soft groaning sound.
                                                  --Spenser.
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   2. To give heed to; to hear attentively. [Archaic]
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            The King of Naples . . . hearkens my brother's suit.
                                                  --Shak.
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   To hearken out, to search out. [Obs.]
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            If you find none, you must hearken out a vein and
            buy.                                  --B. Johnson.
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