Prepare flour (4)
I believe the answer is:
sift
'prepare flour' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sift that I've seen before include "Make fist of filter" , "Distinguish as with a riddle" , "Use fist to pass through perforated container" , "Sort carefully" , "Examine minutely" .)