Fencer's warning (2,5)
I believe the answer is:
en garde
'fencer's warning' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for en garde that I've seen before include "warning of attack" , "Fencer's warning cry" , "Prepare to fence!" , "Angered with opening position in fencing - be alert. (2,5)" , "Get ready to fence" .)