The Collaborative International Dictionary of English v.0.48:

Antiphony \An*tiph"o*ny\, n.; pl. Antiphonies. [See
   Antiphon.]
   1. A musical response; also, antiphonal chanting or signing.
      [1913 Webster]

   2. An anthem or psalm sung alternately by a choir or
      congregation divided into two parts. Also figuratively.
      [1913 Webster]

            O! never more for me shall winds intone,
            With all your tops, a vast antiphony. --R. Browning.
      [1913 Webster]

WordNet (r) 3.0 (2006):

antiphony
    n 1: alternate (responsive) singing by a choir in two parts
    2: a verse or song to be chanted or sung in response [syn:
       antiphon, antiphony]