Trumpet or trombone (4)
I believe the answer is:
horn
I believe this is a double definition.
'trumpet' is the first definition.
(I know that trumpet can be written as horn)
'trombone' is the second definition.
(thesaurus)
(Other definitions for horn that I've seen before include "Hooter" , "Possession of huntsman or deer" , "See 1 Across" , "Cusp" , "Brass musical instrument" .)