Perhaps cow is to appear menacing (5)

I believe the answer is:

lower

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'perhaps cow' is the definition.

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

(Other definitions for lower that I've seen before include "Inferior - scowl" , "Threaten" , "Farther down" , "Lessen" , "put down" .)

I've seen this clue in The Sun.

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