Facts turned to some great advantage (4)
I believe the answer is:
data
'facts' is the definition.
(thesaurus)
'turned to some great advantage' is the wordplay.
'turned' shows that the letters should be reversed in order.
'to some' indicates a hidden word (some of the parts of the word are used).
'atad' is hidden in the letters of 'great advantage'.
'atad' written backwards gives 'DATA'.
(Other definitions for data that I've seen before include "Listed facts" , "Contents of some banks?" , "Facts and statistics collected together" , "Raw facts" , "tables, perhaps" .)