The Collaborative International Dictionary of English v.0.48:

Depositor \De*pos"i*tor\ (d[-e]*p[o^]z"[i^]*t[~e]r), n. [L., fr.
   deponere. See Depone.]
   One who makes a deposit, especially of money in a bank; --
   the correlative of depository.
   [1913 Webster]

WordNet (r) 3.0 (2006):

depositor
    n 1: a person who has deposited money in a bank or similar
         institution