Touch instrument that's blown up (4)
I believe the answer is:
abut
'touch' is the definition.
(abutting is a kind of touching)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for abut that I've seen before include "Meet" , "Lean against the odd tuba" , "Adjoin, touch" , "Lie next to" , "Be next door to" .)