Catholic sits in silence taking Latin discipline (7)
I believe the answer is:
science
'discipline' is the definition.
(science is a kind of discipline)
'catholic sits in silence taking latin' is the wordplay.
'catholic' becomes 'c' (abbreviation as in RC for Roman Catholic).
'sits in' indicates putting letters inside.
'taking' indicates named letters should be taken away.
'latin' becomes 'l'.
'silence' with 'l' taken out is 'sience'.
'c' going within 'sience' is 'SCIENCE'.
(Other definitions for science that I've seen before include "Eg, physics, biology" , "Study of physical things by observation and experiment" , "Branch of study of the physical world" , "Eg, chemistry, physics" , "Organised body of knowledge" .)