Crossword Genius

An outside number that's unidentified (4)

Ross

I believe the answer is:

anon

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

'number that's unidentified' is the definition.
I can't judge whether this defines the answer.

'an outside' is the wordplay.
'an' becomes 'a'.
'outside' becomes 'non'.
'a'+'non'='ANON'

Can you help me to learn more?

(Other definitions for anon that I've seen before include "At another time, of old" , "Soon - nobody knows me" , "Having no known name" , "Shortly; unknown" , "soon to be written" .)

I've seen this clue in The Globe and Mail.
Want a hint initially instead of a full solution? Install my app