1. To remove some material, such as chaff, from grain by means of a current of air: Modern machines can winnow away all the chaff very efficiently. The farmers winnow the chaff away by flinging the grain into the air with a large blanket.
2. To get rid of some unfit or undesirable part; eliminate something or someone: The process will winnow away the weakest candidates. The editor winnowed most of the errors away.
3. To reduce some group by separating or eliminating the unfit or undesirable part: The process winnowed away the field of candidates.
4. To remove some material from a mixture by means of a current of air or water: The wind has winnowed away the sand from the soil. Water currents pick up mud from the riverbank and winnow it away, exposing the rock.