Unexciting sort of note (4)

I believe the answer is:

flat

I believe this is a double definition.

'unexciting' is the first definition.
(I've seen this before)

'sort of note' is the second definition.
(type of musical note)

(Other definitions for flat that I've seen before include "Horizontal" , "Featureless" , "Dull; apartment" , "Even - somewhere to live" , "One at a meeting" .)

I've seen this clue in The Times.

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