Unqualified character on the staff (4)

I believe the answer is:

flat

I believe this clue is a double definition.

'unqualified' is the first definition.
('flat' can be similar in meaning to 'unqualified')

'character on the staff' is the second definition.
(I've seen this before)

(Other definitions for flat that I've seen before include "like some races" , "In music, below the correct pitch" , "Apartment; even" , "12 [TWO DIMENSIONAL]" , "Level - uninteresting - accommodation" .)

I've seen this clue in The Times.

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