Definify.com

Webster 1913 Edition

Verb.

[1st pref.

un-

pay

To undo, take back, or annul, as a payment.

Shak.

, v.t.

To undo. [Not in use.]

Not to pay or compensate. [Not used.]

unpay ‎(third-person singular simple present unpays, present participle unpaying, simple past and past participle unpaid)

To undo, take back, or annul, as a payment.
(Can we find and add a quotation of Shakespeare to this entry?)