Enhance glowing piece about French king with duke (9)
I believe the answer is:
'enhance' is the definition.
'glowing piece about french king with duke' is the wordplay.
'glowing piece' becomes 'ember' (glowing remnant of a fire).
'about' means one lot of letters goes inside another.
'french king' becomes 'roi' ('king' in French).
'with' is a charade indicator (letters next to each other).
'duke' becomes 'd' (abbreviation).
'ember' placed around 'roid' is 'EMBROIDER'.
(Other definitions for embroider that I've seen before include "Ornament with needlework" , "Add (fictitious) detail to" , "Sew; embellish" , "Dress up" , "Do decorative needlework" .)