Inappropriate entry of oboe: very loud (3)
I believe the answer is:
off
'inappropriate' is the definition.
Both the answer and definition are adjectives. Perhaps you can see a link between them that I don't see?
'entry of oboe very loud' is the wordplay.
'entry of' suggests taking the first letters.
'very loud' becomes 'ff' (musical abbreviation).
The initial letter of 'oboe' is 'o'.
'o'+'ff'='OFF'
Can you help me to learn more?
(Other definitions for off that I've seen before include "Gone away or gone stale" , "Far from fresh" , "start to race" , "Discontinued" , "High; cancelled" .)