Source : Webster's Revised Unabridged Dictionary (1913)

Broker \Bro"ker\ (br[=o]"k[~e]r), n. [OE. brocour, from a word
   akin to broken, bruken, to use, enjoy, possess, digest, fr.
   AS. br[=u]can to use, enjoy; cf. Fries. broker, F.
   brocanteur. See {Brook}, v. t.]
   1. One who transacts business for another; an agent.

   2. (Law) An agent employed to effect bargains and contracts,
      as a middleman or negotiator, between other persons, for a
      compensation commonly called brokerage. He takes no
      possession, as broker, of the subject matter of the
      negotiation. He generally contracts in the names of those
      who employ him, and not in his own. --Story.

   3. A dealer in money, notes, bills of exchange, etc.

   4. A dealer in secondhand goods. [Eng.]

   5. A pimp or procurer. [Obs.] --Shak.

   {Bill broker}, one who buys and sells notes and bills of
      exchange.

   {Curbstone broker} or {Street broker}, an operator in stocks
      (not a member of the Stock Exchange) who executes orders
      by running from office to office, or by transactions on
      the street. [U.S.]

   {Exchange broker}, one who buys and sells uncurrent money,
      and deals in exchanges relating to money.

   {Insurance broker}, one who is agent in procuring insurance
      on vessels, or against fire.

   {Pawn broker}. See {Pawnbroker}.

   {Real estate broker}, one who buys and sells lands, and
      negotiates loans, etc., upon mortgage.

   {Ship broker}, one who acts as agent in buying and selling
      ships, procuring freight, etc.

   {Stock broker}. See {Stockbroker}.

Source : WordNet®

broker
     n : a businessman who buys or sells for another in exchange for
         a commission [syn: {agent}, {factor}]
     v : act as a broker

Source : Free On-Line Dictionary of Computing

broker
     
        {object request broker}