To winnow is to cut a big group down to a small one by throwing away the parts you don't want, so that only the good part is left. A company gets 300 job applications and winnows them down to ten people to interview. A judge winnows fifty entries down to three. You usually say winnow down (winnow the list down to five) or winnow out (winnow out the weak ideas — here the thing you name is what you REMOVE). This word carries a picture with it. The old meaning, still alive on farms, is what a farmer does after cutting wheat: he throws the grain up in the air, the wind blows the light useless skin (the chaff) away, and the heavy good seed falls back down. So when someone says winnow, there is a feeling that the bad stuff is light and empty and the good stuff has real weight, and that some process — not just personal taste — is doing the separating. Because of that picture, winnow sounds a bit careful and a bit slow, like real work is being done. It is a written word more than a spoken one: you meet it in news reports, business writing, and school writing far more than in daily talk. A friend would just say "we cut the list down". It is not formal in a cold way, though — writers like it because it is vivid.

篩選、去蕪存菁（把名單、人選一層層刷掉，留下少數）；原意是農人揚穀，把穀殼吹走留下穀粒