Something like pea-soup? (3)

I believe the answer is:

fog

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'soup?' is the definition.
(thesaurus)

I don't understand the remainder of the clue.

(Other definitions for fog that I've seen before include "Miasma" , "Bank restricting visibility" , "Impenetrable mist" , "Bafflement" , "Pea-souper" .)

I've seen this clue in the Evening Standard.

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