The conclusion is oppressive (5)
I believe the answer is:
close
I believe this clue is a double definition.
'the conclusion' is the first definition.
('close' can be a synonym of 'conclusion')
'oppressive' is the second definition.
(I've seen this in another clue)
'is' acts as a link.
(Other definitions for close that I've seen before include "Near; bring to an end" , "Shut - sultry" , "Imminent" , "Not far off" , "Cessation" .)