to throw something loose into the air so it spreads out: to winnow grain, and by extension to scatter people or strew objects far and wide
At its root this word pictures a single physical action: taking something loose in the hand and flinging it up so the wind carries it and it settles apart. On a threshing floor that action is winnowing, tossing the crushed grain into the evening breeze so the light chaff blows away and the heavy kernels fall back in a clean heap. Every other use grows out of that picture.
When the thing being flung is not grain but a nation, the same word describes exile: God scatters a rebellious people among foreign lands the way a farmer scatters chaff to the wind, so that they no longer form one heap but are strewn thin across the earth. This is the most frequent use, and it is almost always a threat of judgment. When the thing flung is dust, ash, fire, or dung, the word simply means to strew or fling it out over a surface.
A fourth use turns the picture inward. Because winnowing is an act of sorting, separating what is worth keeping from what is worthless, the word can mean to sift or scrutinize: a wise king winnows out the wicked from among the good, and God is said to winnow a person's path, meaning he examines it closely and knows it through and through.
The senses are close cousins, so translators pick the English word that fits the object in view (winnow, scatter, disperse, strew, sift). No single English verb covers the whole range, which is why the same Hebrew word appears in so many guises across English Bibles.