Source : Webster's Revised Unabridged Dictionary (1913)

Retainer \Re*tain"er\, n.
   1. One who, or that which, retains.

   2. One who is retained or kept in service; an attendant; an
      adherent; a hanger-on.

   3. Hence, a servant, not a domestic, but occasionally
      attending and wearing his master's livery. --Cowell.

   4. (Law)
      (a) The act of a client by which he engages a lawyer or
          counselor to manage his cause.
      (b) The act of withholding what one has in his hands by
          virtue of some right.
      (c) A fee paid to engage a lawyer or counselor to maintain
          a cause, or to prevent his being employed by the
          opposing party in the case; -- called also {retaining
          fee}. --Bouvier. --Blackstone.

Source : WordNet®

retainer
     n 1: a fee charged in advance to retain the services of someone
          [syn: {consideration}]
     2: a person working in the service of another (especially in
        the household) [syn: {servant}]
     3: a dental appliance that holds teeth (or a prosthesis) in
        position after orthodontic treatment