Cat born in vault (4)
I believe the answer is:
tomb
'vault' is the definition.
(I've seen this before)
'cat born' is the wordplay.
'cat' becomes 'tom' (a tom is a male cat).
'born' becomes 'b' (abbreviation next to the year of someone's birth).
'tom'+'b'='TOMB'
'in' acts as a link.
(Other definitions for tomb that I've seen before include "remains here" , "Sepulchral monument" , "Catacomb" , "grave situation" , "Underground vault" .)