Person nominally uncertain (7)

I believe the answer is:

another

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'uncertain' is the definition.
Both the definition and answer are adjectives. Maybe you can see an association between them that I don't see?

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for another that I've seen before include "encore?" , "Player or person not yet named or selected" , "A further (item)" , "Somebody else" , "On earth (anag.)" .)

I've seen this clue in the Evening Standard.

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