Stupid way Cymbeline ends? (5)

I believe the answer is:

inane

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'stupid' is the definition.
(I've seen this before)

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

(Other definitions for inane that I've seen before include "Foolish, fatuous" , "Puerile" , "Stupid and silly" , "Dull-witted" , "Foolish, silly" .)

I've seen this clue in The Times.

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