Party that we have outside causes smell (5)
I believe the answer is:
odour
'smell' is the definition.
(I know that smell can be written as odour)
'party that we have outside' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'that we have' becomes 'our' (I can't justify this - if you can you should give a lot more credence to this answer).
'outside' is an insertion indicator.
'do' inserted inside 'our' is 'ODOUR'.
'causes' is the link.
Can you help me to learn more?
(Other definitions for odour that I've seen before include "Aroma, smell" , "Small, aroma" , "for the nose to detect" , "Distinctive smell" , "Nasty smell" .)