The Collaborative International Dictionary of English v.0.48:

Antiphon \An"ti*phon\, n. [LL. antiphona, fr. Gr. ?. See
   Anthem.]
   1. A musical response; alternate singing or chanting. See
      Antiphony, and Antiphone.
      [1913 Webster]

   2. A verse said before and after the psalms. --Shipley.
      [1913 Webster]

WordNet (r) 3.0 (2006):

antiphon
    n 1: a verse or song to be chanted or sung in response [syn:
         antiphon, antiphony]

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "antiphon":
   Agnus Dei, Benedicite, Gloria, Gloria Patri, Gloria in Excelsis,
   Introit, Magnificat, Miserere, Nunc Dimittis, Te Deum, Trisagion,
   Vedic hymn, acknowledgment, alleluia, answer, answering, anthem,
   antiphonal chanting, antiphony, back answer, back talk, backchat,
   canticle, chant, chorale, comeback, doxology, echo, evasive reply,
   hallelujah, hosanna, hymn, hymn of praise, hymnody, hymnography,
   hymnology, laud, mantra, motet, offertory, offertory sentence,
   paean, psalm, psalmody, reaction, ready reply, receipt, rejoinder,
   repartee, replication, reply, report, repost, rescript,
   rescription, respond, respondence, response, responsion,
   responsory, responsory report, retort, return, reverberation,
   riposte, short answer, snappy comeback, versicle, witty reply,
   witty retort, yes-and-no answer