Judo level (3)
I believe the answer is:
dan
'judo level' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for dan that I've seen before include "Judo level of proficiency (3)" , "Man's name; judo grade" , "Dark and damp." , "Proficient combative sportsman" , "Grade of judo black belt" .)