Rear; support (4)
I believe the answer is:
back
I believe this is a double definition.
'rear' is the first definition.
(I know that rear can be written as back)
'support' is the second definition.
(to back is to support or endorse)
(Other definitions for back that I've seen before include "Golf holes 10-18" , "bet" , "Give support to; player" , "defensive player" , "Fashionable again" .)