From The Collaborative International Dictionary of English v.0.48:
Thank \Thank\, v. t. [imp. & p. p. Thanked; p. pr. & vb. n.
Thanking.] [AS. [thorn]ancian. See Thank, n.]
To express gratitude to (anyone) for a favor; to make
acknowledgments to (anyone) for kindness bestowed; -- used
also ironically for blame.
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"Graunt mercy, lord, that thank I you," quod she.
--Chaucer.
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I thank thee for thine honest care. --Shak.
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Weigh the danger with the doubtful bliss,
And thank yourself if aught should fall amiss.
--Dryden.
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