The Collaborative International Dictionary of English v.0.48:
Winnow \Win"now\ (w[i^]n"n[-o]), v. t. [imp. & p. p. Winnowed
(w[i^]n"n[-o]d); p. pr. & vb. n. Winnowing.] [OE. windewen,
winewen, AS. windwian; akin to Goth. winpjan (in comp.),
winpi-skauro a fan, L. ventilare to fan, to winnow; cf. L.
wannus a fan for winnowing, G. wanne, OHG. wanna. [root]131.
See Wind moving air, and cf. Fan., n., Ventilate.]
1. To separate, and drive off, the chaff from by means of
wind; to fan; as, to winnow grain.
Ho winnoweth barley to-night in the threshing floor.
2. To sift, as for the purpose of separating falsehood from
truth; to separate, as bad from good.
Winnow well this thought, and you shall find
This light as chaff that flies before the wind.
3. To beat with wings, or as with wings.[Poetic]
Now on the polar winds; then with quick fan
Winnows the buxom air. --Milton.