The Collaborative International Dictionary of English v.0.48:

Seller \Sell"er\, n.
   One who sells. --Chaucer.
   [1913 Webster]

WordNet (r) 3.0 (2006):

seller
    n 1: someone who promotes or exchanges goods or services for
         money [syn: seller, marketer, vender, vendor,
         trafficker]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "seller":
   agent, chandler, clerk, colporteur, dealer, drummer, fishmonger,
   floorwalker, hawker, ironmonger, merchant, peddler, rep,
   representative, retailer, sales agent, sales engineer, sales force,
   sales manager, sales personnel, salesclerk, salesgirl, saleslady,
   salesman, salespeople, salesperson, saleswoman, scalper,
   selling agent, shop assistant, shop clerk, shopkeeper, store clerk,
   sutler, ticket scalper, traveller, vendor



Bouvier's Law Dictionary, Revised 6th Ed (1856):

SELLER, contracts. One who disposes of a thing in consideration of money; a
vendor.
     2. This term is more usually applied in the sale of chattels, that of
vendor in the sale of estates.
     3. The duties of the seller are, 1. To deal with fairness. 2. To
deliver the thing sold at the time and place appointed, and to take care of
it until delivery; but when everything the seller has to do with the goods
is complete, the property and the risk of accident to the goods, rests in
the buyer, even before delivery, or payment. Noy's Max. ch. 24; 7 East, 571;
2 Bl. Com. 448.  3. To warrant the title of personal property when he sells
it as his own, when it is in his possession. 2 Kent, Com. 374; 1 Lord Raym.
593; 1 Salk. 210.
     4. The rights of the seller are, 1. To be paid the price agreed upon.
2. To be indemnified for any expenses he may have incurred to preserve the
thing sold for the buyer, after the title to it has passed to the latter. 3.
To stop the thing in transitu when the buyer has failed and the price has
not been paid. See Stoppage, in transitu. Vide Purchaser, and the
authorities there cited; Bouv. Inst. Index, h.t.