Source : Webster's Revised Unabridged Dictionary (1913)

Orison \Or"i*son\, n. [OF. orison, oreson, oreison, F. oraison,
   fr. L. oratio speech, prayer. See {Oration}.]
   A prayer; a supplication. [Poetic] --Chaucer. Shak.

         Lowly they bowed, adoring, and began Their orisons,
         each morning duly paid.                  --Milton.

Source : WordNet®

orison
     n : reverent petition to a deity [syn: {prayer}, {petition}]