A month of military music (5)
I believe the answer is:
march
I believe this clue is a double definition.
'a month' is the first definition.
(I know that 3. month is a type of month)
'military music' is the second definition.
(thesaurus)
'of' acts as a link.
(Other definitions for march that I've seen before include "Military walking style" , "Walk smartly" , "Stride; month" , "Month - proceed" , "demo" .)