to free (grain) from the lighter particles of chaff, dirt, etc., especially by throwing it into the air and allowing the wind or a forced current of air to blow away impurities.
2.
to drive or blow (chaff, dirt, etc.) away by fanning.
3.
to blow upon; fan.
4.
to subject to some process of separating or distinguishing; analyze critically; sift: to winnow a mass of statements.
5.
to separate or distinguish (valuable from worthless parts) (sometimes followed by out): to winnow falsehood from truth.