Dull uniform (4)

I believe the answer is:

flat

This clue is a double definition.

'dull' is the first definition.
(similar in meaning)

'uniform' is the second definition.
(I've seen this in other clues)

(Other definitions for flat that I've seen before include "Pressing implement" , "rooms exactly" , "In music, below the correct pitch" , "12 [TWO DIMENSIONAL]" , "Digs perhaps" .)

I've seen this clue in The Globe and Mail.

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