Military flute (4)
I believe the answer is:
fife
'military flute' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for fife that I've seen before include "Historic Scottish county, bordering on the Firth of Forth" , "High-pitched flute played in drum bands" , "Type of flute: Scottish council area" , "Scottish division" , "Small shrill flute" .)