Coming from the rector is one prayer (6)
I believe the answer is:
orison
'prayer' is the definition.
(I know that prayer can be written as orison)
'coming from the rector is one' is the wordplay.
'coming from' indicates the answer is hidden within the clue.
'ORISON' is hidden in the letters of 'rector is one'.
(Other definitions for orison that I've seen before include "An archaic or literary prayer" , "O, no, sir, it makes a prayer" , "Prayer - O no sir! (anag)" , "Supplication" .)