Stake behind hairstyle of an old woman (7)
I believe the answer is:
dowager
'an old woman' is the definition.
(I know this)
'stake behind hairstyle' is the wordplay.
'stake' becomes 'wager' (synonyms).
'behind' means one lot of letters go next to another.
'hairstyle' becomes 'do' (a hairdo).
'wager' put after 'do' is 'DOWAGER'.
'of' acts as a link.
(Other definitions for dowager that I've seen before include "woman of status" , "Titled widow" , "Wealthy old woman" , "One of 16 [OLD GIRLS]" , "Rich old girl" .)