Get well on top (7)
I believe the answer is:
recover
'get well' is the definition.
(thesaurus)
'on top' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'top' becomes 'cover ' (synonyms).
're'+'cover'='RECOVER'
(Other definitions for recover that I've seen before include "Get well again" , "Rally, get better" , "comeback" , "Recuperate" , "Rescue" .)