Source : Webster's Revised Unabridged Dictionary (1913)

Vespers \Ves"pers\, n. pl. [OF. vespres, F. v[^e]pres, LL.
   vesperae, fr. L. vespera evening. See {Vesper}, n.] (R. C.
   Ch.)
   (a) One of the little hours of the Breviary.
   (b) The evening song or service.

   {Sicilian vespers}. See under {Sicilian}, a.

Source : WordNet®

vespers
     n : the sixth of the seven canonical hours of the divine office;
         early evening; now often made a public service on Sundays
         [syn: {evensong}]