Crossword Genius

Wide, costly piano exchanged for tuba, initially (9)

Ross

I believe the answer is:

extensive

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'wide' is the definition.
(similar in meaning)

I cannot understand how the rest of the clue works.

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(Other definitions for extensive that I've seen before include "Far-reaching, wide" , "Covering much area" , "Comprehensive" , "Widespread" , "Covering a wide area" .)

I've seen this clue in The Telegraph.
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