This noun refers to the dry, lightweight chaff separated from grain during the threshing and winnowing process. In agricultural practice, after grain was beaten to separate kernels from stalks, the mixture was tossed into the air so wind could blow away the useless chaff while heavier grain fell back to the threshing floor. Both New Testament occurrences appear in John the Baptist's preaching, where he uses this vivid agricultural image to describe divine judgment. The Messiah will thoroughly winnow his threshing floor, gathering wheat into the barn but burning the chaff 'with unquenchable fire' (Matt 3:12; Luke 3:17). This image of permanent separation and destruction would have been immediately clear to an agricultural audience.