Endlessly fill hours working and do well (8)
I believe the answer is:
flourish
'do well' is the definition.
(thesaurus)
'endlessly fill hours working' is the wordplay.
'endlessly' means to remove the last letter.
'working' is an anagram indicator.
'fill' with its final letter taken away is 'fil'.
'fil'+'hours'='filhours'
'filhours' anagrammed gives 'FLOURISH'.
'and' is the link.
(Other definitions for flourish that I've seen before include "Grow vigorously and healthily" , "Fanfare!" , "Wax" , "Large vase, pot" , "Bloom" .)