Crossword Genius

A manic nun mithered a northerner (9)

Ross

I believe the answer is:

mancunian

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

'a northerner' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps there's a link between them I don't understand?

'a manic nun mithered' is the wordplay.
'a manic nun' can be anagrammed to 'MANCUNIAN'.
But, I am not sure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for mancunian that I've seen before include "Native of Manchester" , "citizen" .)

I've seen this clue in The Independent.
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