Means of preserving grim impartiality (7)

I believe the answer is:

candour

'impartiality' is the definition.
(candour is a kind of impartiality)

'means of preserving grim' is the wordplay.
'means of preserving' becomes 'can' (cans preserve food).
'grim' becomes 'dour' (synonyms).
'can'+'dour'='CANDOUR'

(Other definitions for candour that I've seen before include "Artlessness" , "Frankness, openness" , "telling it like it is" , "Openness, honesty" , "open)" .)

I've seen this clue in The Guardian.

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