Assist, aid (4)
I believe the answer is:
help
This clue is a double definition.
'assist' is the first definition.
(I know that assist can be written as help)
'aid' is the second definition.
(I know that aid can be written as help)
(Other definitions for help that I've seen before include "Beatles single" , "Beatles' album; assist" , "Take what you want" , "Assist, aid" , "Serve" .)