Liberal extracted from dark side (4)
I believe the answer is:
back
'side' is the definition.
(I know that back is a type of side)
'liberal extracted from dark' is the wordplay.
'liberal' becomes 'l' (abbreviation).
'extracted from' indicates named letters should be taken away.
'dark' becomes 'black' (similar in meaning).
'black' with 'l' removed is 'BACK'.
(Other definitions for back that I've seen before include "Rear; spine" , "ago" , "Support - football player" , "Rear -- endorse" , "Support - defender - reverse" .)