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.
      [1913 Webster]

   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.
      [1913 Webster]

   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]

The Collaborative International Dictionary of English v.0.48:

Winnow \Win"now\, v. i.
   To separate chaff from grain.
   [1913 Webster]

         Winnow not with every wind.              --Ecclus. v.
                                                  9.
   [1913 Webster]

WordNet (r) 3.0 (2006):

winnow
    n 1: the act of separating grain from chaff; "the winnowing was
         done by women" [syn: winnow, winnowing, sifting]
    v 1: separate the chaff from by using air currents; "She stood
         there winnowing chaff all day in the field" [syn: winnow,
         fan]
    2: blow on; "The wind was winnowing her hair"; "the wind
       winnowed the grass"
    3: select desirable parts from a group or list; "cull out the
       interesting letters from the poet's correspondence"; "winnow
       the finalists from the long list of applicants" [syn: cull
       out, winnow]
    4: blow away or off with a current of air; "winnow chaff"

Moby Thesaurus II by Grady Ward, 1.0:

123 Moby Thesaurus words for "winnow":
   aerate, air, air out, air-condition, air-cool, airify, analyze,
   appraise, assess, bolt, catalog, categorize, choose out, clarifier,
   clarify, class, classify, clear, colander, comb, contradistinguish,
   cordon, cordon off, cradle, cribble, cross-ventilate, cull,
   cull out, decide between, decrassify, demarcate, demark, depurate,
   differentiate, discriminate, distill, distinguish, divide,
   draw the line, edulcorate, elute, essentialize, evaluate, excerpt,
   extract, factor, fan, filter, filtrate, freshen, gauge, ghettoize,
   gin, glean, group, handpick, identify, insulate, isolate,
   keep apart, keep aside, lay aside, leach, lixiviate, lixiviator,
   make a selection, mark the interface, oxygenate, oxygenize,
   percolate, percolator, pick, pick out, purifier, purify, put aside,
   quarantine, rectify, refine, refiner, refinery, refresh, riddle,
   rocker, ruffle, screen, screen out, seclude, segregate, select,
   separate, set a limit, set apart, set aside, set off, sever,
   severalize, sieve, sieve out, sift, sift out, sifter, single out,
   sort, sort out, spiritualize, split hairs, strain, strainer,
   subdivide, sublimate, sublime, subtilize, thrash, thrash out,
   thresh, try, ventilate, weigh, wind, winnowing basket,
   winnowing fan, winnowing machine



Easton's 1897 Bible Dictionary:

Winnow
   Corn was winnowed, (1.) By being thrown up by a shovel against
   the wind. As a rule this was done in the evening or during the
   night, when the west wind from the sea was blowing, which was a
   moderate breeze and fitted for the purpose. The north wind was
   too strong, and the east wind came in gusts. (2.) By the use of
   a fan or van, by which the chaff was blown away (Ruth 3:2; Isa.
   30:24; Jer. 4:11, 12; Matt. 3:12).