The Collaborative International Dictionary of English v.0.48:
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. [1913 Webster] Lowly they bowed, adoring, and began Their orisons, each morning duly paid. --Milton. [1913 Webster]WordNet (r) 3.0 (2006):
orison n 1: reverent petition to a deity [syn: prayer, petition, orison]