Massive endless vault with nasty smell (5)
I believe the answer is:
jumbo
'massive' is the definition.
(synonyms)
'endless vault with nasty smell' is the wordplay.
'endless' means to remove the last letter.
'vault' becomes 'jump' (vault can mean to jump).
'with' is a charade indicator (letters next to each other).
'nasty smell' becomes 'B.O.' (abbreviation for body odour).
'jump' with its last letter removed is 'jum'.
'jum'+'bo'='JUMBO'
(Other definitions for jumbo that I've seen before include "Elephant(ine)" , "Big jet" , "Unusually large" , "Enormous" , "Huge (plane or elephant?)" .)