Vault, bound (4)
I believe the answer is:
leap
I believe this is a double definition.
'vault' is the first definition.
(I've seen this in another clue)
'bound' is the second definition.
(synonyms)
(Other definitions for leap that I've seen before include "as 1984 was" , "'Look before you . . . .'" , "Jump; type of year" , "Jump, spring" , "some years?" .)