Avoid drill sergeant’s shouted command (4)

I believe the answer is:

shun

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'avoid' is the definition.
(I know that shun is a is a more specific form of the action avoid)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for shun that I've seen before include "Parade-ground language" , "Avoid, keep away from" , "Avoid - attention!" , "Keep away from, have nothint to do with" , "Spurn; avoid" .)

I've seen this clue in The Times.

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