Repay (r-p), v. t. [imp. & p. p. Repaid (-pd); p. pr. & vb. n. Repaying.]
Etymology: [Pref. re- + pay: cf. F. repayer.]
1. To pay back; to refund; as, to repay money borrowed or advanced. If you repay me not on such a day, In such a place, such sum or sums. Shak.
2. To make return or requital for; to recompense; -- in a good or bad sense; as, to repay kindness; to repay an injury. Benefits which can not be repaid . . . are not commonly found to increase affection. Rambler.
3. To pay anew, or a second time, as a debt.
Syn. -- To refund; restore; return; recompense; compensate; remunerate; satisfy; reimburse; requite.
Shades of meaning
Fernald has no entry of its own for repay; he lists it under requite.
Where he writes about it:
To repay or to retaliate, to punish or to reward, may be to make some return very inadequate to the benefit or injury received, or the right or wrong done; but to requite (according to its etymology) is to make so full and adequate a return as to quit oneself of all obligation of favor or hostility, of punishment or reward. — from requite
Requite is often used in the more general sense of recompense or repay, but always with the suggestion, at least, of the original idea of full equivalent; when one speaks of requiting kindness with ingratitude, the expression gains force from the comparison of the actual with the proper and appropriate return. — from requite