WordNet (r) 3.0 (2006):

matins
    n 1: the first canonical hour; at daybreak [syn: matins,
         morning prayer]

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "matins":
   AM, Ack Emma, Mass, ante meridiem, bedtime prayer, camp meeting,
   church, church service, compline, devotions, divine service, duty,
   evening devotions, evensong, exercises, foreday, forenoon,
   grey-eyed morn, incense-breathing morn, lauds, liturgy, meeting,
   morn, morning, morning devotions, morning time, morntime,
   night song, none, nones, novena, office, praise meeting, prayer,
   prayer meeting, prayers, prime, prime song, public worship,
   revival, revival meeting, service, sext, tent meeting, this AM,
   this morning, tierce, undersong, vesper, vespers, vigils,
   waking time, watch meeting, watch night, watch-night service