The Collaborative International Dictionary of English v.0.48:

Debtee \Debt*ee"\, n. (Law)
   One to whom a debt is due; creditor; -- correlative to
   debtor. --Blackstone.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

DEBTEE. One to whom a debt is due a creditor, as, debtee executor. 3 Bl.
Com. 18.