Not completely headstrong prince (3)
I believe the answer is:
ras
'prince' is the definition.
(I've seen this before)
'not completely headstrong' is the wordplay.
'not completely' means to remove the last letter (the word is incomplete).
'headstrong' becomes 'rash' (I've seen this before).
'rash' with its final letter taken off is 'RAS'.
(Other definitions for ras that I've seen before include "prince from Ethiopia" , "Ethiopian prince" , "Abyssinian prince" , "headland" , "Cape" .)