Instrument on plane, extremely rough in motion? (9)
I believe the answer is:
alpenhorn
'instrument' is the definition.
(I know that alpenhorn is a instrument)
'on plane extremely rough in motion?' is the wordplay.
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'in motion?' indicates an anagram (I've seen this in other clues).
'rough' with its middle removed is 'rh'.
'on'+'plane'+'rh'='onplanerh'
'onplanerh' is an anagram of 'ALPENHORN'.
(Other definitions for alpenhorn that I've seen before include "What plays (over the heads of many)" , "blown up" , "Swiss wind instrument" , "It's a blast" , "Instrument for communication" .)