The Collaborative International Dictionary of English v.0.48:

Trader \Trad"er\, n.
   1. One engaged in trade or commerce; one who makes a business
      of buying and selling or of barter; a merchant; a
      trafficker; as, a trader to the East Indies; a country
      trader.
      [1913 Webster]

   2. A vessel engaged in the coasting or foreign trade.
      [1913 Webster]

WordNet (r) 3.0 (2006):

trader
    n 1: someone who purchases and maintains an inventory of goods
         to be sold [syn: trader, bargainer, dealer, monger]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "trader":
   broker, businessman, buyer, chandler, dealer, distributor,
   importer, jobber, marketer, merchandiser, merchant, middleman,
   monger, purchaser, regrater, retail dealer, retail merchant,
   retailer, salesman, salesperson, saleswoman, seller, shopkeeper,
   storekeeper, tradesman, tradeswoman, trafficker, vendor,
   wholesaler