Emissions from SEAT and Triumph 500 (4)
I believe the answer is:
wind
'emissions from seat' is the definition.
(flatulence)
'triumph 500' is the wordplay.
'triumph' becomes 'win' (a win is a victory or triumph).
'500' becomes 'D' (Roman numeral for 500).
'win'+'d'='WIND'
'and' is the link.
(Other definitions for wind that I've seen before include "Air-current" , "Take turns" , "Mistral, for example, or sirocco" , "take course that's not straightforward? Doesn't sound like it" , "Meaningless talk; twist" .)