Calm, settle Catholic, if accommodated (6)
I believe the answer is:
pacify
'calm' is the definition.
(I know this)
'settle catholic if accommodated' is the wordplay.
'settle' becomes 'pay' (paying is a kind of settling).
'catholic' becomes 'C' (abbreviation as in RC for Roman Catholic).
'accommodated' means one lot of letters goes inside another.
'c'+'if'='cif'
'pay' enclosing 'cif' is 'PACIFY'.
(Other definitions for pacify that I've seen before include "Quell the anger of" , "Make calmer" , "Make calm, soothe" , "Quieten" , "Bring peace to (a place)" .)