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]