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]

Moby Thesaurus II by Grady Ward, 1.0:

108 Moby Thesaurus words for "anthem":
   Agnus Dei, Benedicite, Brautlied, Christmas carol, Gloria,
   Gloria Patri, Gloria in Excelsis, Introit, Kunstlied, Liebeslied,
   Magnificat, Miserere, Negro spiritual, Nunc Dimittis, Te Deum,
   Trisagion, Vedic hymn, Volkslied, alba, alleluia, answer, antiphon,
   antiphony, art song, aubade, ballad, ballade, ballata, barcarole,
   blues, blues song, boat song, bridal hymn, brindisi, calypso,
   canso, cantata, canticle, canzone, canzonet, canzonetta, carol,
   cavatina, chanson, chant, chantey, chorale, church music, croon,
   croon song, dirge, ditty, doxology, drinking song, epithalamium,
   folk song, gospel, gospel music, hallelujah, hosanna, hymeneal,
   hymn, hymn of praise, hymn-tune, hymnody, hymnography, hymnology,
   introit, laud, lay, lied, lilt, love song, love-lilt, mantra, mass,
   matin, minstrel song, minstrelsy, motet, national anthem,
   offertory, offertory sentence, oratorio, paean, passion, prosodion,
   prothalamium, psalm, psalmody, recessional, report, requiem,
   requiem mass, response, responsory, sacred music, serena, serenade,
   serenata, song, spiritual, theme song, torch song, versicle,
   war song, wedding song, white spiritual