Speak of sin restraining love (5)
I believe the answer is:
'speak' is the definition.
(to voice something is to say it)
'sin restraining love' is the wordplay.
'sin' becomes 'vice'.
'restraining' is an insertion indicator.
'love' becomes 'o' (love means zero in tennis).
'vice' placed around 'o' is 'VOICE'.
'of' acts as a link.
(Other definitions for voice that I've seen before include "Sound produced in speaking" , "Speak of - mouthpiece" , "tenor, say" , "Sound of speaker" , "Wallop" .)