Duck, sweetheart! (4)
I believe the answer is:
love
This clue is a double definition.
'duck' is the first definition.
(duck and love can mean zero in sports)
'sweetheart' is the second definition.
(both are terms of address to romantic partner)
(Other definitions for love that I've seen before include "Precious" , "1970 film, starring Ali MacGraw and Ryan O'Neal" , "Zero score, dear" , "Score of zero at tennis" , "God of 20 Dn" .)