Sway on the brink (6)
I believe the answer is:
teeter
'sway on the brink' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for teeter that I've seen before include "Seesaw, totter" , "Rock unsteadily on edge" , "Hesitate on the brink" , "Sway, as if about to fall" , "See-saw on the edge" .)