Talk of love rat with energy (5)
I believe the answer is:
orate
'talk' is the definition.
(to orate is to give a speech)
'love rat with energy' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'with' says to put letters next to each other.
'energy' becomes 'e' (physics symbol as in E=mc2).
'o'+'rat'+'e'='ORATE'
'of' is the link.
(Other definitions for orate that I've seen before include "Speak formally" , "Speechify" , "Talk pompously" , "talk at length" , "Spout" .)