Abuts in a way that is unusual, but instrumental (5)

I believe the answer is:

tubas

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'is unusual but instrumental' is the definition.
I can't tell whether this defines the answer.

'abuts in a way' is the wordplay.
'in a way' indicates anagramming the letters.
'abuts' anagrammed gives 'TUBAS'.

'that' is the link.

Can you help me to learn more?

(Other definitions for tubas that I've seen before include "What some musicians" , "Large brass instruments" .)

I've seen this clue in the Evening Standard.

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