Abundant in flu bout, sadly (9)
I believe the answer is:
bountiful
'abundant' is the definition.
(thesaurus)
'in flu bout sadly' is the wordplay.
'sadly' indicates an anagram.
'in'+'flu'+'bout'='influbout'
'influbout' with letters rearranged gives 'BOUNTIFUL'.
(Other definitions for bountiful that I've seen before include "flush with bonus for joining up?" , "So-called lady" , "Ample or generous (Lady!)" , "Generous in giving -- abundant" , "Giving generously" .)