The Collaborative International Dictionary of English v.0.48:

Agnus Dei \Ag"nus De"i\ [L., lamb of God.] (R. C. Ch.)
   (a) A figure of a lamb bearing a cross or flag.
   (b) A cake of wax stamped with such a figure. It is made from
       the remains of the paschal candles and blessed by the
       Pope.
   (c) A triple prayer in the sacrifice of the Mass, beginning
       with the words "Agnus Dei."
       [1913 Webster]

WordNet (r) 3.0 (2006):

Agnus Dei
    n 1: figure of a lamb; emblematic of Christ [syn: Agnus Dei,
         Paschal Lamb]
    2: a liturgical prayer beginning with these Latin words

Moby Thesaurus II by Grady Ward, 1.0:

118 Moby Thesaurus words for "Agnus Dei":
   Alleluia, Anamnesis, Benedicite, Blessing, Canon, Collect,
   Communion, Consecration, Credo, Dismissal, Epistle, Fraction,
   Gloria, Gloria Patri, Gloria in Excelsis, Gospel, Gradual,
   Holy Grail, Host, Introit, Kyrie, Kyrie Eleison, Last Gospel,
   Lavabo, Magnificat, Miserere, Nunc Dimittis, Offertory,
   Paternoster, Pax, Pieta, Post-Communion, Preface, Sanctus,
   Sanctus bell, Sangraal, Secreta, Te Deum, Tersanctus, Tract,
   Trisagion, Vedic hymn, alleluia, answer, anthem, antiphon,
   antiphony, ark, asperger, asperges, aspergillum, bambino, beadroll,
   beads, candle, canticle, censer, chant, chaplet, chorale, ciborium,
   cross, crucifix, cruet, doxology, eucharistial, hallelujah,
   holy cross, holy water, holy-water sprinkler, hosanna, hymn,
   hymn of praise, hymnody, hymnography, hymnology, icon, incensory,
   laud, mantra, matzo, menorah, mezuzah, mikvah, monstrance, motet,
   offertory, offertory sentence, osculatory, ostensorium, paean,
   paschal candle, pax, phylacteries, prayer shawl, prayer wheel,
   psalm, psalmody, pyx, relics, report, response, responsory, rood,
   rosary, sacramental, sacred relics, sacring bell, shofar, sukkah,
   tabernacle, tallith, thurible, urceole, veronica, versicle,
   vigil light, votive candle