Observe slight upset, not the reverse (7)

I believe the answer is:

obverse

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'the reverse' is the definition.
(thesaurus)

'observe slight upset not' is the wordplay.
'observe' anagrams to 'OBVERSE'.
Though, I am unsure how this is indicated.

Can you help me to learn more?

(Other definitions for obverse that I've seen before include "Side of coin that bears principal design or head" , "One side of a coin" , "Verbose on the opposite side" , "Side of a coin with the main design" , "Side of coin that shows the principal design" .)

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

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