Just plain silly (5)

I believe the answer is:

inane

'just plain silly' is the definition.
(I've seen this in another clue)

This is all the clue.

(Other definitions for inane that I've seen before include "Lacking meaning" , "Silly, witless" , "Devoid of intelligence" , "Foolish, silly" , "Stupid and silly" .)

I've seen this clue in the Universal and The New York Times.

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