The Collaborative International Dictionary of English v.0.48:

Caterer \Ca"ter*er\, n.
   One who caters.
   [1913 Webster]

         The little fowls in the air have God for Their provider
         and caterer.                             --Shelton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

caterer
    n 1: someone who provides food and service (as for a party)

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "caterer":
   chandler, commissariat, commissary, donor, furnisher, manciple,
   merchant, patron, provider, provisioner, purveyor, quartermaster,
   retailer, steward, stock clerk, storekeeper, supplier, sutler,
   victualer, vivandier