Fine work detail (4)
I believe the answer is:
fact
'detail' is the definition.
(thesaurus)
'fine work' is the wordplay.
'fine' becomes 'f' (abbreviation e.g. condition of old coins, books).
'work' becomes 'act' (synonyms).
'f'+'act'='FACT'
(Other definitions for fact that I've seen before include "Something indisputable" , "Datum" , "An indisputable truth" , "given" , "It's certainly not fiction" .)