Composer shown way outside having great knowledge (7)
I believe the answer is:
learned
'having great knowledge' is the definition.
(I've seen this before)
'composer shown way outside' is the wordplay.
'composer' becomes 'arne' (I've seen this in other clues).
'shown way' becomes 'led' (lead can mean to show someone the way).
'outside' means one lot of letters goes inside another.
'arne' put within 'led' is 'LEARNED'.
(Other definitions for learned that I've seen before include "Highbrow" , "Picked up - well-read" , "Having great knowledge" , "Gained understanding" , "Came to know" .)