A hostile measure (3,5)
I believe the answer is:
war dance
'a hostile measure' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'measure' is the wordplay.
I cannot really understand how this works, but
'measure' could be 'dance' (I've seen this before) and 'dance' is present in the answer.
The remaining letters 'war' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for war dance that I've seen before include "Steps taken by fighters" , "steps taken before engagement" , "moves anticipating conflict?" , "Pre-battle ceremony" , "Tribal ceremony before battle" .)