Humour achieving sublimity during May? (4)

I believe the answer is:

jest

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'humour' is the definition.
(jest is a kind of humour)

I don't understand the rest of the clue.

(Other definitions for jest that I've seen before include "Joke, gag" , "it's not serious, so to speak" , "Joke, fool about" , "Piece of humour" , "Sally" .)

I've seen this clue in the Evening Standard.

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