Arbitrary assertion (3-2)

I think it could be either:

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3-2

say-so

'arbitrary assertion' is the definition.
(I've seen this before)

This is the entire clue.

(Other definitions for say-so that I've seen before include "Authority - rumour" , "Authority to make a decision" , "Authorisation" , "Go-ahead" , "Authority to make or allow something to happen" .)

I've seen this clue in The Mirror.

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