A sally (6)
I believe the answer is:
sortie
'a sally' is the definition.
(I know that sally can be written as sortie)
This is all the clue.
(Other definitions for sortie that I've seen before include "Raid - short trip" , "Operational flight by a bomber or fighter" , "Short foray" , "Short trip; attack" , "Warplane's flight" .)