Obscene imperial measure (5)

I believe the answer is:

gross

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This clue could be a double definition.

'obscene' is the first definition.
(thesaurus)

'imperial measure' is the second definition.
'gross' can be an answer for 'measure' (gross is a kind of measure). I am not certain of the 'imperial' bit.

Can you help me to learn more?

(Other definitions for gross that I've seen before include "Flagrant - unpleasant - 144" , "exclamation of disgust" , "Coarse; repulsive" , "square?" , "Description of crude" .)

I've seen this clue in The Times.

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