Silly idiots, ninnies and nincompoops: empty heads (5)

I believe the answer is:

inane

'silly' is the definition.
(thesaurus)

'idiots ninnies and nincompoops empty heads' is the wordplay.
'heads' suggests taking the first letters.
The initial letters of 'idiots ninnies and nincompoops empty' is 'INANE'.

(Other definitions for inane that I've seen before include "Thick" , "Foolish, silly" , "Fatuous, mindless" , "Empty" , "Frivolous" .)

I've seen this clue in The Telegraph.

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