The Collaborative International Dictionary of English v.0.48:

Stockjobber \Stock"job`ber\, n. [Stock + job.]
   One who speculates in stocks for gain; one whose occupation
   is to buy and sell stocks. In England a jobber acts as an
   intermediary between brokers.
   [1913 Webster]

WordNet (r) 3.0 (2006):

stockjobber
    n 1: one who deals only with brokers or other jobbers