Book about what Serena Williams might do (7)
I believe the answer is:
reserve
'book' is the definition.
(as in booking or reserving in advance)
'about what serena williams might do' is the wordplay.
I cannot quite see how this works, but
'about' could be 're' ('re' means regarding or about) and 're' is present in the answer.
'do' could be 'serve' (synonyms) and 'serve' is found within the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for reserve that I've seen before include "Lack of openness" , "Bank" , "Set aside - shyness" , "Wine kept" , "put to one side" .)