Golden Rule preposition (4)
I believe the answer is:
unto
'golden rule preposition' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for unto that I've seen before include "To old" , "To (obs.)" , "'''For ... us a child is born'' (Handel's Messiah) (4)'" , "'The Lord said . . . . Moses'" , "'Do ... others, etc.'" .)