The Collaborative International Dictionary of English v.0.48:

Jobber \Job"ber\, n.
   1. One who works by the job.
      [1913 Webster]

   2. A dealer in the public stocks or funds; a stockjobber.
      [Eng.]
      [1913 Webster]

   3. One who buys goods from importers, wholesalers, or
      manufacturers, and sells to retailers.
      [1913 Webster]

   4. One who turns official or public business to private
      advantage; hence, one who performs low or mercenary work
      in office, politics, or intrigue.
      [1913 Webster]

WordNet (r) 3.0 (2006):

jobber
    n 1: someone who buys large quantities of goods and resells to
         merchants rather than to the ultimate customers [syn:
         jobber, middleman, wholesaler]

Moby Thesaurus II by Grady Ward, 1.0:

88 Moby Thesaurus words for "jobber":
   Wall Streeter, agent, blue-collar worker, bond crowd, breadwinner,
   broker, casual, casual laborer, chandler, common laborer,
   connection, curb broker, day laborer, dealer, distributor,
   employee, factory worker, floor broker, floor trader, floorman,
   flunky, free lance, free-lancer, full-time worker, go-between,
   hand, importer, industrial worker, intermediary, intermedium,
   jobholder, laborer, laboring man, liaison, link, marketer, mediary,
   mediator, medium, menial, merchandiser, merchant, middleman,
   migrant, moiler, monger, navvy, odd-lot dealer, office temporary,
   pit man, proletarian, registered representative, regrater,
   retail dealer, retail merchant, retailer, roustabout,
   salaried worker, self-employed person, servant, sharebroker,
   shopkeeper, specialist, stiff, stock dealer, stock-exchange broker,
   stockbroker, stockjobber, storekeeper, temporary, tie, toiler,
   trader, tradesman, tradeswoman, trafficker, two-dollar broker,
   wage earner, wage slave, wageworker, wholesaler, worker, workgirl,
   workhand, working girl, workingman, workingwoman, workman



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

JOBBER, commerce. One who buys end sells articles for others. Stock jobbers
are those who buy, and sell stocks for others; this term is also applied to
those who speculate in stocks on their own account.