Madam Antoinette, somewhat unyielding (7)
I believe the answer is:
adamant
'unyielding' is the definition.
(I've seen this in another clue)
'madam antoinette somewhat' is the wordplay.
'somewhat' indicates the answer is hidden within the clue.
'ADAMANT' can be found hidden inside 'madam antoinette'.
(Other definitions for adamant that I've seen before include "Unyielding to requests, stubborn" , "Resolute, refusing to yield" , "Unyielding, won't change mind" , "Unshakable (in an opinion)" , "Unpersuadable" .)