A quiet, flexible Catholic entered as a candidate (9)
I believe the answer is:
applicant
'a candidate' is the definition.
(I've seen this before)
'a quiet flexible catholic entered' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'flexible' becomes 'pliant' (similar in meaning).
'catholic' becomes 'C' (abbreviation as in RC for Roman Catholic).
'entered' means one lot of letters goes inside another.
'pliant' placed around 'c' is 'plicant'.
'a'+'p'+'plicant'='APPLICANT'
'as' is the link.
(Other definitions for applicant that I've seen before include "Person attempting to get a job" , "one looking for a job" , "Job seeker" , "Candidate for a post" , "Job-seeker" .)