Religious writings brought up - bishop is under some pressure (4)
I believe the answer is:
torr
'some pressure' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'religious writings brought up bishop is under' is the wordplay.
'religious writings' becomes 'ot' (I am not sure about this - if you are sure you should believe this answer much more).
'brought up' is a reversal indicator (in a down clue, letters go up).
'bishop' becomes 'rr' (abbreviation for Right Reverend).
'is under' says to put letters next to each other (in a down clue, some letters go below others).
'ot' back-to-front is 'to'.
'to'+'rr'='TORR'
Can you help me to learn more?
(Other definitions for torr that I've seen before include "Pressure unit equivalent to 1 mm of mercury" , "Unit of very low pressure" , "Height" .)