Quick to show a professional’s not upset (6)

I believe the answer is:

pronto

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'quick' is the definition.
Both the answer and definition are adverbs. Perhaps they are linked in a way I don't understand?

'a professional's not upset' is the wordplay.
'a professional' becomes 'pro' ('pro' can be a synonym of 'professional').
'upset' is an anagram indicator.
'not' is an anagram of 'nto'.
'pro'+'nto'='PRONTO'

'to show' is the link.

Can you help me to learn more?

(Other definitions for pronto that I've seen before include "Promptly, without delay" , "Italian telephonic greeting" , "Right away, quickly" , "Quickly (sl.)" , "Immediately, amigo" .)

I've seen this clue in the Evening Standard.

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