Unwilling chap entered in further exam (9)
I believe the answer is:
resistant
'unwilling' is the definition.
(thesaurus)
'chap entered in further exam' is the wordplay.
'chap' becomes 'stan'.
'entered in' means one lot of letters goes inside another.
'further exam' becomes 'resit' (I've seen this before).
'stan' inserted into 'resit' is 'RESISTANT'.
(Other definitions for resistant that I've seen before include "Hindering the conductor" , "not accommodating" , "Impervious (to corrosion, heat, etc)" , "holding out" , "tough" .)