The Collaborative International Dictionary of English v.0.48:

Debtor \Debt"or\, n. [OE. dettur, dettour, OF. detor, detur,
   detour, F. d['e]biteur, fr. L. debitor, fr. debere to owe.
   See Debt.]
   One who owes a debt; one who is indebted; -- correlative to
   creditor.
   [1913 Webster]

         [I 'll] bring your latter hazard back again,
         And thankfully rest debtor for the first. --Shak.
   [1913 Webster]

         In Athens an insolvent debtor became slave to his
         creditor.                                --Mitford.
   [1913 Webster]

         Debtors for our lives to you.            --Tennyson.
   [1913 Webster]

WordNet (r) 3.0 (2006):

debtor
    n 1: a person who owes a creditor; someone who has the
         obligation of paying a debt [syn: debtor, debitor]
         [ant: creditor]