Less than average state (4)

I believe the answer is:

aver

I'm a little stuck... Click here to teach me more about this clue!

'state' is the definition.
(both can mean to declare)

I cannot understand how the rest of the clue works.

(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.

Want a hint initially instead of a full solution? Install my app