The Collaborative International Dictionary of English v.0.48:

Hedge \Hedge\, n. [OE. hegge, AS. hecg; akin to haga an
   inclosure, E. haw, AS. hege hedge, E. haybote, D. hegge, OHG.
   hegga, G. hecke. [root]12. See Haw a hedge.]
   A thicket of bushes, usually thorn bushes; especially, such a
   thicket planted as a fence between any two portions of land;
   and also any sort of shrubbery, as evergreens, planted in a
   line or as a fence; particularly, such a thicket planted
   round a field to fence it, or in rows to separate the parts
   of a garden.
   [1913 Webster]

         The roughest berry on the rudest hedge.  --Shak.
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         Through the verdant maze
         Of sweetbrier hedges I pursue my walk.   --Thomson.
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   Note: Hedge, when used adjectively or in composition, often
         means rustic, outlandish, illiterate, poor, or mean;
         as, hedge priest; hedgeborn, etc.
         [1913 Webster]

   Hedge bells, Hedge bindweed (Bot.), a climbing plant
      related to the morning-glory (Convolvulus sepium).

   Hedge bill, a long-handled billhook.

   Hedge garlic (Bot.), a plant of the genus Alliaria. See
      Garlic mustard, under Garlic.

   Hedge hyssop (Bot.), a bitter herb of the genus Gratiola,
      the leaves of which are emetic and purgative.

   Hedge marriage, a secret or clandestine marriage,
      especially one performed by a hedge priest. [Eng.]

   Hedge mustard (Bot.), a plant of the genus Sisymbrium,
      belonging to the Mustard family.

   Hedge nettle (Bot.), an herb, or under shrub, of the genus
      Stachys, belonging to the Mint family. It has a
      nettlelike appearance, though quite harmless.

   Hedge note.
   (a) The note of a hedge bird.
   (b) Low, contemptible writing. [Obs.] --Dryden.

   Hedge priest, a poor, illiterate priest. --Shak.

   Hedge school, an open-air school in the shelter of a hedge,
      in Ireland; a school for rustics.

   Hedge sparrow (Zool.), a European warbler (Accentor
      modularis) which frequents hedges. Its color is reddish
      brown, and ash; the wing coverts are tipped with white.
      Called also chanter, hedge warbler, dunnock, and
      doney.

   Hedge writer, an insignificant writer, or a writer of low,
      scurrilous stuff. [Obs.] --Swift.

   To breast up a hedge. See under Breast.

   To hang in the hedge, to be at a standstill. "While the
      business of money hangs in the hedge." --Pepys.
      [1913 Webster]

WordNet (r) 3.0 (2006):

hedge mustard
    n 1: stiffly branching Old World annual with pale yellow
         flowers; widely naturalized in North America; formerly used
         medicinally [syn: hedge mustard, Sisymbrium officinale]