The Collaborative International Dictionary of English v.0.48:

Heath \Heath\ (h[=e]th), n. [OE. heth waste land, the plant
   heath, AS. h[=ae][eth]; akin to D. & G. heide, Icel.
   hei[eth]r waste land, Dan. hede, Sw. hed, Goth. hai[thorn]i
   field, L. bucetum a cow pasture; cf. W. coed a wood, Skr.
   ksh[=e]tra field. [root]20.]
   1. (Bot.)
      (a) A low shrub (Erica vulgaris or Calluna vulgaris),
          with minute evergreen leaves, and handsome clusters of
          pink flowers. It is used in Great Britain for brooms,
          thatch, beds for the poor, and for heating ovens. It
          is also called heather, and ling.
      (b) Also, any species of the genus Erica, of which
          several are European, and many more are South African,
          some of great beauty. See Illust. of Heather.
          [1913 Webster]

   2. A place overgrown with heath; any cheerless tract of
      country overgrown with shrubs or coarse herbage.
      [1913 Webster]

            Their stately growth, though bare,
            Stands on the blasted heath.          --Milton
      [1913 Webster]

   Heath cock (Zool.), the blackcock. See Heath grouse
      (below).

   Heath grass (Bot.), a kind of perennial grass, of the genus
      Triodia (Triodia decumbens), growing on dry heaths.

   Heath grouse, or Heath game (Zool.), a European grouse
      (Tetrao tetrix), which inhabits heaths; -- called also
      black game, black grouse, heath poult, heath fowl,
      moor fowl. The male is called heath cock, and
      blackcock; the female, heath hen, and gray hen.

   Heath hen. (Zool.) See Heath grouse (above).

   Heath pea (Bot.), a species of bitter vetch (Lathyrus
      macrorhizus), the tubers of which are eaten, and in
      Scotland are used to flavor whisky.

   Heath throstle (Zool.), a European thrush which frequents
      heaths; the ring ouzel.
      [1913 Webster]

WordNet (r) 3.0 (2006):

heath pea
    n 1: European herb bearing small tubers used for food and in
         Scotland to flavor whiskey [syn: heath pea, earth-nut
         pea, earthnut pea, tuberous vetch, Lathyrus
         tuberosus]