The Collaborative International Dictionary of English v.0.48:

Debit \Deb"it\, n. [L. debitum what is due, debt, from debere to
   owe: cf. F. d['e]bit. See Debt.]
   A debt; an entry on the debtor (Dr.) side of an account; --
   mostly used adjectively; as, the debit side of an account.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Debit \Deb"it\, v. t. [imp. & p. p. Debited; p. pr. & vb. n.
   Debiting.]
   1. To charge with debt; -- the opposite of, and correlative
      to, credit; as, to debit a purchaser for the goods sold.
      [1913 Webster]

   2. (Bookkeeping) To enter on the debtor (Dr.) side of an
      account; as, to debit the amount of goods sold.
      [1913 Webster]

WordNet (r) 3.0 (2006):

debit
    n 1: an accounting entry acknowledging sums that are owing [syn:
         debit, debit entry] [ant: credit, credit entry]
    v 1: enter as debit [ant: credit]