Treason upsets him (7)

I believe the answer is:

senator

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'him' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.

'treason upsets' is the wordplay.
'upsets' indicates an anagram.
'treason' anagrammed gives 'SENATOR'.

Can you help me to learn more?

(Other definitions for senator that I've seen before include "Treason committed by member of Upper House" , "Treason by member of parliament" , "Member of the Upper House of the US Congress" , "Member of the Second House" , "One from uni's governing body" .)

I've seen this clue in the Evening Standard.

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