Support; pair (5)
I believe the answer is:
brace
I believe this is a double definition.
'support' is the first definition.
(I know that brace is a type of structural member)
'pair' is the second definition.
(I know that pair can be written as brace)
(Other definitions for brace that I've seen before include "Strengthening piece" , "Support - pair" , "Pair - strut" , "prepare for impact" , "Support; two" .)