Such a tune has a droning accompaniment (7)

I believe the answer is:

bagpipe

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'accompaniment' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for bagpipe that I've seen before include "Reed instrument" , "Instrument 4 [THE SCOTTISH PLAY]" , "Traditional Scottish musical instrument" , "Musical instrument associated with Scotland" .)

I've seen this clue in the Evening Standard.

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