Arguably middle-sized instrument for battle (6,7)
I believe the answer is:
little bighorn
'battle' is the definition.
Both the answer and definition are singular nouns.
Maybe there's a link between them I don't understand?
'arguably middle-sized instrument' is the wordplay.
I cannot quite see how this works, but
'instrument' could be 'horn' (horn is a kind of instrument) and 'horn' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'for' is the link.
Can you help me to learn more?
(Other definitions for little bighorn that I've seen before include "native American success" , "Custer's final battle" , "Scene of Custer's Last Stand, 1876" , "Site of Custer's defeat" .)