One who vacillates (7)
I believe the answer is:
waverer
'one who vacillates' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for waverer that I've seen before include "Shilly-shallier" , "Irresolute person" , "One who can't make up his mind" , "One who is irresolute" , "One who vacillates" .)