Supports or reinforces (8)
I believe the answer is:
bolsters
This clue is a double definition.
'supports' is the first definition.
('bolster' can be a synonym of 'support')
'reinforces' is the second definition.
(bolstering is a kind of reinforcing)
(Other definitions for bolsters that I've seen before include "Long pillows or supports for lobsters" , "Supports and strengthens, props up" , "Supports with big pillows" , "Long under-pillows" .)