Lacking intelligence (6)

I think it could be either:

Which length description are you looking for?:

stupid

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

This is all the clue.

(Other definitions for stupid that I've seen before include "Not intelligent, thick" , "Asinine" , "Not sensible or intelligent" , "dope" , "Barmy" .)

I've seen this clue in The Telegraph and The Times.

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