By concealing a standing charge that's hefty (5)
I believe the answer is:
beefy
'hefty' is the definition.
(thesaurus)
'by concealing a standing charge' is the wordplay.
'concealing' is an insertion indicator.
'a standing' shows that the letters should be reversed in order (in a down clue, letters stand up).
'charge' becomes 'fee' (fee is a kind of charge).
'fee' reversed gives 'eef'.
'by' enclosing 'eef' is 'BEEFY'.
'that's' acts as a link.
(Other definitions for beefy that I've seen before include "like some bully?" , "Burly" , "Brawny" , "Muscular, robust" , "Colloquially muscular" .)