Musical instrument degrees - about the limit? (7)

I believe the answer is:

marimba

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'musical instrument' is the definition.
(I know that marimba is a type of percussion instrument)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for marimba that I've seen before include "Form of xylophone" , "Xylophone-like instr." , "African xylophone" , "Xylophone-like instrument from Africa" , "Jazz instrument" .)

I've seen this clue in The Independent.

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