Valved brass instrument (4)
(Other definitions for tuba that I've seen before include "Brass "oompah" instrument" , "It's not top brass" , "member of band" , "Valved instrument" , "Brass band instrument" .)
(Other definitions for french horn that I've seen before include "Brass musical instrument" , "Wind instrument" , "part of a broken-down 27 [CARTHORSE]?" .)