Religious instruction for Catholic? Problem is Mass without English (9)
I believe the answer is:
catechism
'religious instruction for catholic?' is the definition.
(question and answer method of religious teaching)
'problem is mass without english' is the wordplay.
'problem' becomes 'catch' (I have seen 'Hidden problem' mean 'catch' so perhaps 'problem' could also mean 'catch').
'mass' becomes 'm' (symbol used in Physics e.g. f=ma).
'without' is an insertion indicator ('without' can be similar in meaning to 'outside').
'english' becomes 'e' (abbreviation).
'catch'+'is'+'m'='catchism'
'catchism' placed around 'e' is 'CATECHISM'.
(Other definitions for catechism that I've seen before include "summary of belief" , "Schematic for religious questions-and-answers book" , "Set of questions for religious teaching" , "Schematic for summary of religious principles" , "Schematic for religious principles in question and answer format" .)