Close to harm? It’s horribly grim (11)

I believe the answer is:

nightmarish

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

'close to harm? it's horribly' is the wordplay.
'close to' becomes 'nigh' (I've seen this in another clue).
'horribly' indicates an anagram (a horribly wrong version of the letters).
'harm'+'its'='harmits'
'harmits' is an anagram of 'tmarish'.
'nigh'+'tmarish'='NIGHTMARISH'

Can you help me to learn more?

(Other definitions for nightmarish that I've seen before include "Very scary" , "Like a bad dream" , "Terrifying" , "horrible" , "Frightening, unpleasant" .)

I've seen this clue in the Sydney Morning Herald.

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