No score in tennis (4)
I believe the answer is:
love
'no score in tennis' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for love that I've seen before include ""Tell me the truth about ___" (Auden)" , "Deep affection" , "powerful emotion" , "Adore, cherish" , "All you need, according to the song" .)