Authority is silent? (3-2)

I believe the answer is:

say-so

'authority' is the definition.
(I know that authority can be written as say-so)

I don't understand how the remainder of the clue works.

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

I've seen this clue in The Times.

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