In a bad temper when overturned (5)

I believe the answer is:

upset

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'overturned' is the definition.
(I know that overturned can be written as upset)

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

Can you help me to learn more?

(Other definitions for upset that I've seen before include "Overturn; distress" , "Discountenanced" , "Overturn; unhappy" , "bug" , "Surprise - distress" .)

I've seen this clue in The Globe and Mail.

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