Disciplinarian (8)

I believe the answer is:
martinet
'disciplinarian' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for martinet that I've seen before include "Person who demands strict obedience" , "Tyrant, one who demands strict obedience" , "Gradgrind was one" , "Strict disciplinarian - met train (anag)" , "Disciplined type" .)