Source : Webster's Revised Unabridged Dictionary (1913)

Bivalve \Bi"valve\, a. [Pref. bi- + valve.] (Zo["o]l. & Bot.)
   Having two shells or valves which open and shut, as the
   oyster and certain seed vessels.

Bivalve \Bi"valve\, n. [F. bivalve; bi- (L. bis) + valve valve.]
   1. (Zo["o]l.) A mollusk having a shell consisting of two
      lateral plates or valves joined together by an elastic
      ligament at the hinge, which is usually strengthened by
      prominences called teeth. The shell is closed by the
      contraction of two transverse muscles attached to the
      inner surface, as in the clam, -- or by one, as in the
      oyster. See Mollusca.

   2. (Bot.) A pericarp in which the seed case opens or splits
      into two parts or valves.

Source : WordNet®

bivalve
     adj : used of mollusks having two shells (as clams etc.) [syn: {bivalved}]
           [ant: {univalve}]

bivalve
     n : marine or freshwater mollusks having a soft body with
         platelike gills enclosed within two shells hinged
         together [syn: {pelecypod}, {lamellibranch}]