Figurehead to take the stage in reality (4)
I believe the answer is:
fact
'in reality' is the definition.
(thesaurus)
'figurehead to take the stage' is the wordplay.
'figurehead' becomes 'f' (head letter of 'figure').
'to take the stage' becomes 'act' (I've seen this in another clue).
'f'+'act'='FACT'
(Other definitions for fact that I've seen before include "True statement" , "Statement of verifiable information" , "Fait accompli" , "An indisputable truth" , "given" .)