The Collaborative International Dictionary of English v.0.48:

Banker \Bank"er\ (b[a^][ng]k"[~e]r), n.[See the nouns Bank and
   the verbs derived from them.]
   1. One who conducts the business of banking; one who,
      individually, or as a member of a company, keeps an
      establishment for the deposit or loan of money, or for
      traffic in money, bills of exchange, etc.
      [1913 Webster]

   2. A money changer. [Obs.]
      [1913 Webster]

   3. The dealer, or one who keeps the bank in a gambling house.
      [1913 Webster]

   4. A vessel employed in the cod fishery on the banks of
      Newfoundland. --Crabb. --J. Q. Adams.
      [1913 Webster]

   5. A ditcher; a drain digger. [Prov. Eng.]
      [1913 Webster]

   6. The stone bench on which masons cut or square their work.
      --Weale.
      [1913 Webster]

WordNet (r) 3.0 (2006):

banker
    n 1: a financier who owns or is an executive in a bank
    2: the person in charge of the bank in a gambling game

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "banker":
   Shylock, bank clerk, bank manager, bank officer, bank president,
   banking executive, baron, big boss, big businessman, bill broker,
   business leader, businessman, cambist, captain of industry,
   cashier, director, discounter, enterpriser, entrepreneur,
   financier, industrialist, investment banker, king, lender,
   little businessman, loan officer, loan shark, loaner, magnate,
   man of commerce, manager, money broker, money changer,
   money dealer, moneylender, moneymonger, mortgage holder, mortgagee,
   note broker, pawnbroker, teller, top executive, trust officer,
   tycoon, usurer



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

BANKER, com. law. A banker is one engaged in the business of receiving other
persons money in deposit, to be returned on demand discounting other
persons' notes, and issuing his own for circulation. One who performs the
business usually transacted by a bank. Private bankers are generally not
permitted.
     2. The business of bankers is generally performed through the medium of
incorporated banks.
     3. A banker may be declared a bankrupt by adverse proceedings against
him. Act of Congress of 19th Aug. 1841. See 1  Atk. 218; 2 H. Bl. 235; 1
Mont. B. L. 12.
     4. Among the ancient Romans there were bankers called argentarii, whose
office was to keep registers of contracts between individuals, either to
loan money, or in relation to sales and stipulations. These bankers
frequently agreed with the creditor to pay him the debt due to him by the
debtor. Calvini Lex. Jurid.