Not all are convinced (7)

I believe the answer is:

certain

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

'are convinced' is the definition.
(similar in meaning)

I don't understand the rest of the clue.

(Other definitions for certain that I've seen before include "Sure, definite" , "Indisputable" , "Convinced" , "Nice art (anag)" , "Quite sure, positive" .)

I've seen this clue in the Evening Standard.

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