Two in support (5)
I believe the answer is:
brace
I believe this is a double definition.
'two' is the first definition.
(brace is a kind of two)
'support' is the second definition.
(I know that brace is a type of support)
'in' is the link.
(Other definitions for brace that I've seen before include "Pair of game-birds" , "double" , "Tighten, strengthen" , "Stanchion" , "Strengthener; pair" .)