Wide, costly piano exchanged for tuba, initially (9)
I believe the answer is:
extensive
'wide' is the definition.
(similar in meaning)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for extensive that I've seen before include "Far-reaching, wide" , "Covering much area" , "Comprehensive" , "Widespread" , "Covering a wide area" .)