Oppressive; tacky (6)
I believe the answer is:
sticky
This clue is a double definition.
'oppressive' is the first definition.
(I've seen this before)
'tacky' is the second definition.
(I've seen this before)
(Other definitions for sticky that I've seen before include "sultry?" , "Difficult - adhesive" , "Awkward; tacky" , "Adhesive, gluey" , "Close" .)