The Collaborative International Dictionary of English v.0.48:

Witch \Witch\, n. [OE. wicche, AS. wicce, fem., wicca, masc.;
   perhaps the same word as AS. w[imac]tiga, w[imac]tga, a
   soothsayer (cf. Wiseacre); cf. Fries. wikke, a witch, LG.
   wikken to predict, Icel. vitki a wizard, vitka to bewitch.]
   [1913 Webster]
   1. One who practices the black art, or magic; one regarded as
      possessing supernatural or magical power by compact with
      an evil spirit, esp. with the Devil; a sorcerer or
      sorceress; -- now applied chiefly or only to women, but
      formerly used of men as well.
      [1913 Webster]

            There was a man in that city whose name was Simon, a
            witch.                                --Wyclif (Acts
                                                  viii. 9).
      [1913 Webster]

            He can not abide the old woman of Brentford; he
            swears she's a witch.                 --Shak.
      [1913 Webster]

   2. An ugly old woman; a hag. --Shak.
      [1913 Webster]

   3. One who exercises more than common power of attraction; a
      charming or bewitching person; also, one given to
      mischief; -- said especially of a woman or child.
      [Colloq.]
      [1913 Webster]

   4. (Geom.) A certain curve of the third order, described by
      Maria Agnesi under the name versiera.
      [1913 Webster]

   5. (Zool.) The stormy petrel.
      [1913 Webster]

   6. A Wiccan; an adherent or practitioner of Wicca, a
      religion which in different forms may be paganistic and
      nature-oriented, or ditheistic. The term witch applies to
      both male and female adherents in this sense.
      [PJC]

   Witch balls, a name applied to the interwoven rolling
      masses of the stems of herbs, which are driven by the
      winds over the steppes of Tartary. Cf. Tumbleweed.
      --Maunder (Treas. of Bot.)

   Witches' besoms (Bot.), tufted and distorted branches of
      the silver fir, caused by the attack of some fungus.
      --Maunder (Treas. of Bot.)

   Witches' butter (Bot.), a name of several gelatinous
      cryptogamous plants, as Nostoc commune, and Exidia
      glandulosa. See Nostoc.

   Witch grass (Bot.), a kind of grass (Panicum capillare)
      with minute spikelets on long, slender pedicels forming a
      light, open panicle.

   Witch meal (Bot.), vegetable sulphur. See under
      Vegetable.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Panicum capillare
    n 1: North American grass with slender brushy panicles; often a
         weed on cultivated land [syn: witchgrass, witch grass,
         old witchgrass, old witch grass, tumble grass,
         Panicum capillare]