Prior: clergyman in devout environment (8)
I believe the answer is:
previous
'prior' is the definition.
(I've seen this before)
'clergyman in devout environment' is the wordplay.
'clergyman' becomes 'rev' (I've seen this before).
'in' means one lot of letters goes inside another.
'devout environment' becomes 'pious' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'rev' put inside 'pious' is 'PREVIOUS'.
Can you help me to learn more?
(Other definitions for previous that I've seen before include "form" , "Overly hasty in acting or in drawing a conclusion" , "earlier convictions" , "Earlier, occasion say" , "Over-prompt or over-hasty" .)