Male cat, black, in vault (4)
I believe the answer is:
tomb
'vault' is the definition.
(thesaurus)
'male cat black' is the wordplay.
'male cat' becomes 'tom' (I've seen this before).
'black' becomes 'b' (as in pencil classifications).
'tom'+'b'='TOMB'
'in' acts as a link.
(Other definitions for tomb that I've seen before include "Burial site" , "Large vault" , "Place of burial, grave or vault" , "Building for a body" , "Underground vault" .)