The Collaborative International Dictionary of English v.0.48:

Rush \Rush\, n. [OE. rusche, rische, resche, AS. risce, akin to
   LG. rusk, risch, D. & G. rusch; all probably fr. L. ruscum
   butcher's broom; akin to Goth. raus reed, G. rohr.]
   1. (Bot.) A name given to many aquatic or marsh-growing
      endogenous plants with soft, slender stems, as the species
      of Juncus and Scirpus.
      [1913 Webster]

   Note: Some species are used in bottoming chairs and plaiting
         mats, and the pith is used in some places for wicks to
         lamps and rushlights.
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   2. The merest trifle; a straw.
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            John Bull's friendship is not worth a rush.
                                                  --Arbuthnot.
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   Bog rush. See under Bog.

   Club rush, any rush of the genus Scirpus.

   Flowering rush. See under Flowering.

   Nut rush
      (a) Any plant of the genus Scleria, rushlike plants with
          hard nutlike fruits.
      (b) A name for several species of Cyperus having
          tuberous roots.

   Rush broom, an Australian leguminous plant (Viminaria
      denudata), having long, slender branches. Also, the
      Spanish broom. See under Spanish.

   Rush candle, See under Candle.

   Rush grass, any grass of the genus Vilfa, grasses with
      wiry stems and one-flowered spikelets.

   Rush toad (Zool.), the natterjack.

   Scouring rush. (Bot.) Same as Dutch rush, under Dutch.


   Spike rush, any rushlike plant of the genus Eleocharis,
      in which the flowers grow in dense spikes.

   Sweet rush, a sweet-scented grass of Arabia, etc.
      (Andropogon schoenanthus), used in Oriental medical
      practice.

   Wood rush, any plant of the genus Luzula, which differs
      in some technical characters from Juncus.
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WordNet (r) 3.0 (2006):

rush grass
    n 1: grass having wiry stems and sheathed panicles [syn: rush
         grass, rush-grass]