The Collaborative International Dictionary of English v.0.48:
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
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.