Refusal of French knob (4)
I believe the answer is:
node
'knob' is the definition.
(I know that knob can be written as node)
'refusal of french' is the wordplay.
'refusal' becomes 'no' (saying no to something).
'of french' becomes 'de' ('of' in French).
'no'+'de'='NODE'
(Other definitions for node that I've seen before include "Done (anag.); a knot" , "Knob or lump" , "part of network" , "Slight swelling on a plant where new leaves emerge" , "Done to a small lump" .)