The Russian commander's given the push (7)

I believe the answer is:

cossack

(Other definitions for cossack that I've seen before include "Member of Russian, Ukrainian people" , "One of a people from SW Russia, Ukraine" , "One from southern Russia or Ukraine noted for horse riding skills" , "Belligerent Russian" , "One of an elite cavalry corps in tzarist Russia" .)

I've seen this clue in the Evening Standard.

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