Comic opera singer, expert on love (5)
I believe the answer is:
buffo
'comic opera singer' is the definition.
(term for a singer in an opera buffa or comic opera)
'expert on love' is the wordplay.
'expert' becomes 'buff' (I've seen this before).
'on' says to put letters next to each other.
'love' becomes 'o' (In tennis, 'love' means 'zero').
'buff'+'o'='BUFFO'
(Other definitions for buffo that I've seen before include "Burlesque (opera) (It.)" , "opera singer" , "Italian singer" , "style of opera" , "Comic in Italian opera" .)