Cause storm in teacup? (4)

I believe the answer is:

stir

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'cause storm' is the definition.
'stir' can be an answer for 'storm' (thesaurus). I'm unsure of the 'cause' bit.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for stir that I've seen before include "Whisk or mix" , "Commotion; wake" , "Arouse; commotion" , "unrest" , "Commotion - prison" .)

I've seen this clue in The Sun.

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