Have riches perhaps in a vault (6)
I believe the answer is:
abound
'have riches perhaps' is the definition.
(I've seen this before)
'a vault' is the wordplay.
'vault' becomes 'bound' (I've seen this before).
'a'+'bound'='ABOUND'
'in' acts as a link.
(Other definitions for abound that I've seen before include "Be plentiful - take a jump" , "Be in ample supply" , "Exist in large numbers" , "Have riches perhaps" , "Be plentiful, say fish in river" .)