The Collaborative International Dictionary of English v.0.48:

Evensong \E"ven*song`\, n. [AS. [=ae]fensang.]
   A song for the evening; the evening service or form of
   worship (in the Church of England including vespers and
   compline); also, the time of evensong. --Wyclif. Milton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

evensong
    n 1: the sixth of the seven canonical hours of the divine
         office; early evening; now often made a public service on
         Sundays [syn: vespers, evensong]
    2: (Anglican Church) a daily evening service with prayers
       prescribed in the Book of Common Prayer [syn: Evening
       Prayer, evensong]

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "evensong":
   Mass, bedtime prayer, camp meeting, church, church service,
   close of day, cockshut, compline, crepuscular, devotions,
   divine service, dusk, dusky, duty, eve, even, evening,
   evening devotions, eventide, exercises, grayness, lauds, liturgy,
   matins, meeting, morning devotions, night song, nightfall, none,
   nones, novena, office, praise meeting, prayer, prayer meeting,
   prayers, prime, prime song, public worship, revival,
   revival meeting, service, setting sun, sext, shut of day, sundown,
   sunset, sunsetty, tent meeting, the expiring day, tierce, twilight,
   twilighty, undersong, vesper, vespers, vespertine, vigils,
   watch meeting, watch night, watch-night service