Crossword Genius

Mad character in NHS triage not exactly critical (5,10)

Ross

I believe the answer is:

earth shattering

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

'mad character in nhs triage not exactly' is the wordplay.
'mad character' becomes 'hatter' (Alice In Wonderland).
'in' is an insertion indicator.
'not exactly' indicates an anagram.
'nhs'+'triage'='nhstriage'
'nhstriage' with letters rearranged gives 'earthsing'.
'hatter' placed into 'earthsing' is 'EARTH-SHATTERING'.

Can you help me to learn more?

(Other definitions for earth shattering that I've seen before include "Momentous" , "Really big" , "Extremely important" , "great importance" .)

I've seen this clue in The Daily Express.
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