Worthless support (4)
I believe the answer is:
base
This clue is a double definition.
'worthless' is the first definition.
(I've seen this before)
'support' is the second definition.
(I know that base is a type of support)
(Other definitions for base that I've seen before include "floor" , "Plinth" , "This underlying structure" , "Meanspirited" , "Not worth much" .)