Russian cavalryman (7)
I believe the answer is:
cossack
'russian cavalryman' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for cossack that I've seen before include "Warrior peasant of SE Russia" , "Belligerent Russian" , "One from southern Russia or Ukraine noted for horse riding skills" , "Member of Russian, Ukrainian people" , "Member of an elite cavalry in tzarist Russia" .)