Less than average state (4)

I believe the answer is:

aver

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'state' is the definition.
(thesaurus)

I can't explain the rest of the clue.

(Other definitions for aver that I've seen before include "State (to be the case)" , "Swear" , "Assert to be the case" , "State firmly and positively" , "Declare to be the case" .)

I've seen this clue in the Evening Standard.

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