In addition, charity produces sacred songs (6)
I believe the answer is:
psalms
'sacred songs' is the definition.
(psalm is a type of hymn)
'in addition charity' is the wordplay.
'in addition' becomes 'PS' (postscript written at the end of a letter).
'charity' becomes 'alms' (alms is a kind of charity).
'ps'+'alms'='PSALMS'
'produces' acts as a link.
(Other definitions for psalms that I've seen before include "Songs of David" , "in the Bible?" , "Sacred songs of praise" , "Devotional songs" , "Move fast, noisily" .)