Hazy sort of explosion nitrogen's put down (7)

I believe the answer is:

unclear

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'hazy' is the definition.
(thesaurus)

I don't understand how the remainder of the clue works.

(Other definitions for unclear that I've seen before include "Imprecise, hazy" , "Not easy to see or understand" , "An ulcer (anag)" , "Cloudy or opaque" , "Vague" .)

I've seen this clue in The Telegraph.

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