Remove the chaff (6)
I believe the answer is:
thresh
'remove the chaff' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for thresh that I've seen before include "Separate grain from (eg, corn)" , "as one may having crop" , "Separate seed from grain" , "Extract grain (with flail)" , "Separate corn from husks by beating" .)