Disdain incentive, finally stubborn (5)
I believe the answer is:
spurn
'disdain' is the definition.
('spurn' can be a synonym of 'disdain')
'incentive finally stubborn' is the wordplay.
'incentive' becomes 'spur' (I've seen this before).
'finally' indicates one should take the final letters.
The final letter of 'stubborn' is 'n'.
'spur'+'n'='SPURN'
(Other definitions for spurn that I've seen before include "Contemptuously dismiss" , "Reject scornfully, say unwanted suitor" , "Treat with contempt" , "Show contempt for" , "discard" .)