Suspecting obscure fungus almost directly (11)

I believe the answer is:

mistrustful

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'suspecting' is the definition.
(thesaurus)

'obscure fungus almost directly' is the wordplay.
I cannot quite understand how this works, but
'obscure' could be 'mist' (synonyms) and 'mist' is located in the answer.
'fungus' could be 'rust' (rust fungus is a kind of fungus) and 'rust' is found in the answer.
This explanation may well be incorrect...

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I've seen this clue in The Times.

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