Secular origins of Latin arias in church (4)
I believe the answer is:
laic
'secular' is the definition.
(synonyms)
'origins of latin arias in church' is the wordplay.
'origins of' indicates taking the first letters.
The first letters of 'latin arias in church' is 'LAIC'.
(Other definitions for laic that I've seen before include "Of non-clerical people" , "of secular matters" , "Unlike minister" , "people not in church" , "Non-clergy" .)