The Collaborative International Dictionary of English v.0.48:

Bimetallic \Bi`me*tal"lic\, a. [Pref. bi- + metallic: cf. F.
   bim['e]tallique.]
   1. Of or relating to, or using, a double metallic standard
      (as gold and silver) for a system of coins or currency.
      [archaic]
      [1913 Webster]

   2. Composed of two different metals; formed of two parts,
      each of a different metal; as, bimetallic wire; bimetallic
      thermometer, etc.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

bimetallic
    adj 1: pertaining to a monetary system based on two metals; "in
           a bimetallistic system both gold and silver can
           constitute legal tender" [syn: bimetallistic,
           bimetallic]
    2: formed of two different metals or alloys; especially in
       sheets bonded together [syn: bimetal, bimetallic]