The Collaborative International Dictionary of English v.0.48:

Winnowing \Win"now*ing\, n.
   The act of one who, or that which, winnows.
   [1913 Webster]

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.]
   [1913 Webster]
   1. To separate, and drive off, the chaff from by means of
      wind; to fan; as, to winnow grain.
      [1913 Webster]

            Ho winnoweth barley to-night in the threshing floor.
                                                  --Ruth. iii.
                                                  2.
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   2. To sift, as for the purpose of separating falsehood from
      truth; to separate, as bad from good.
      [1913 Webster]

            Winnow well this thought, and you shall find
            This light as chaff that flies before the wind.
                                                  --Dryden.
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   3. To beat with wings, or as with wings.[Poetic]
      [1913 Webster]

            Now on the polar winds; then with quick fan
            Winnows the buxom air.                --Milton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

winnowing
    n 1: the act of separating grain from chaff; "the winnowing was
         done by women" [syn: winnow, winnowing, sifting]