Glib line about a Catholic (6)
I believe the answer is:
facile
'glib' is the definition.
(thesaurus)
'line about a catholic' is the wordplay.
'line' becomes 'file' (file is a kind of line**).
'about' is an insertion indicator.
'catholic' becomes 'c' (abbreviation as in RC for Roman Catholic).
'a'+'c'='ac'
'file' placed around 'ac' is 'FACILE'.
(Other definitions for facile that I've seen before include "Easy to accomplish" , "Effortless, easy" , "Arrived at without due care or effort" , "Smooth" , "Simplistic" .)