Crossword Genius

Part of musical series, apparently one short? (4)

Ross

I believe the answer is:

note

'part of musical series' is the definition.
(musical note)

I cannot understand how the rest of the clue works.

(Other definitions for note that I've seen before include "Heed; record" , "Single tone; short letter" , "Fame - memorandum" , "Memo; piano key" , "Short personal letter" .)

I've seen this clue in The Times.
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