Marched around vault (4)
I believe the answer is:
arch
'vault' is the definition.
(I've seen this in another clue)
'marched around' is the wordplay.
'around' says the answer is hidden in the clue.
'ARCH' is hidden within 'marched'.
(Other definitions for arch that I've seen before include "Consummate" , "(archaic)" , "Knowing, sly" , "Affectedly playful or extreme" , "Wellington's, perhaps" .)