The Collaborative International Dictionary of English v.0.48:

Polyphase \Pol"y*phase\, a. [Poly- + phase.] (Elec.)
   Having or producing two or more phases; multiphase; as, a
   polyphase machine, a machine producing two or more pressure
   waves of electro-motive force, differing in phase; a
   polyphase current.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

polyphase
    adj 1: of an electrical system that uses or generates two or
           more alternating voltages of the same frequency but
           differing in phase angle [syn: multiphase, polyphase]