Leading monk in excellent surroundings in theory (1,6)
I believe the answer is:
a priori
'in theory' is the definition.
Both the answer and definition are adverbs. Maybe you can see a link between them that I don't see?
'leading monk in excellent surroundings' is the wordplay.
I cannot really understand how this works, but
'monk' could be 'prior' (I've seen this in another clue) and 'prior' is present in the answer.
'excellent' could be 'ai' (resembles 'A1', old-fashioned term for excellent) and 'ai' is present in the remaining letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for a priori that I've seen before include "Derived by logic, without observed facts (Latin)" , "Way of reasoning" , "From logic rather than experience" , "(Reasoning) from first principles (Latin)" , "arguing from known facts" .)