Chap with a black belt (3)
I believe the answer is:
dan
'chap' is the definition.
'with a black belt' is the wordplay.
'with' indicates putting letters inside.
'black belt' becomes 'dn' (I can't justify this - if you can you should believe this answer much more).
'a' going inside 'dn' is 'DAN'.
Can you help me to learn more?
(Other definitions for dan that I've seen before include "Karate expert" , "Grade of proficiency in judo" , "Level of proficiency in Japanese martial arts" , "An expert in throws" , "Proficient combative sportsman" .)