The Collaborative International Dictionary of English v.0.48:

Anthem \An"them\ ([a^]n"th[e^]m), n. [OE. antym, antefne, AS.
   antefen, fr. LL. antiphona, fr. Gr. 'anti`fwna, neut. pl. of
   'anti`fwnon antiphon, or anthem, n. neut., from 'anti`fwnos
   sounding contrary, returning a sound; 'anti` over against +
   fwnh` sound, voice: the anthem being sung by the choristers
   alternately, one half-choir answering the other: cf. OF.
   anthaine, anteine, antieune, F. antienne. See Antiphon.]
   1. Formerly, a hymn sung in alternate parts, in present
      usage, a selection from the Psalms, or other parts of the
      Scriptures or the liturgy, set to sacred music.
      [1913 Webster]

   2. A song or hymn of praise or devotion; as, a national
      anthem. --Milton.
      [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Anthem \An"them\, v. t.
   To celebrate with anthems. [Poet.]
   [1913 Webster]

         Sweet birds antheming the morn.          --Keats.
   [1913 Webster]

WordNet (r) 3.0 (2006):

anthem
    n 1: a song of devotion or loyalty (as to a nation or school)
    2: a song of praise (to God or to a saint or to a nation) [syn:
       hymn, anthem]