Madam Antoinette, somewhat unyielding (7)
I believe the answer is:
adamant
'unyielding' is the definition.
(I've seen this before)
'madam antoinette somewhat' is the wordplay.
'somewhat' indicates the answer is hidden within the clue.
'ADAMANT' is hidden in the letters of '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" .)