Bully to conceal leather (7)
I believe the answer is:
cowhide
'leather' is the definition.
(I know that cowhide is a type of leather)
'bully to conceal' is the wordplay.
'bully' becomes 'cow' (cow can mean to bully or oppress).
'to conceal' becomes 'hide' (synonyms).
'cow'+'hide'='COWHIDE'
(Other definitions for cowhide that I've seen before include "Giving leather" , "Type of leather" , "whip" , "neat wrapper?" .)