Joins in a rising smell (5)
I believe the answer is:
knits
'joins' is the definition.
(knitting is a kind of joining)
'a rising smell' is the wordplay.
'a rising' shows that the letters should be reversed in order (going up in a down clue).
'smell' becomes 'stink' (stink is a kind of smell).
'stink' backwards is 'KNITS'.
'in' acts as a link.
(Other definitions for knits that I've seen before include "Stitches" , "Unites" , "Purses" , "Works with needles and wool" .)