The Collaborative International Dictionary of English v.0.48:

Whin \Whin\, n. [W. chwyn weeds, a single weed.]
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   1. (Bot.)
      (a) Gorse; furze. See Furze.
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                Through the whins, and by the cairn. --Burns.
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      (b) Woad-waxed. --Gray.
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   2. Same as Whinstone. [Prov. Eng.]
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   Moor whin or Petty whin (Bot.), a low prickly shrub
      (Genista Anglica) common in Western Europe.

   Whin bruiser, a machine for cutting and bruising whin, or
      furze, to feed cattle on.

   Whin Sparrow (Zool.), the hedge sparrow. [Prov. Eng.]

   Whin Thrush (Zool.), the redwing. [Prov. Eng.]
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WordNet (r) 3.0 (2006):

petty whin
    n 1: prickly yellow-flowered shrub of the moors of New England
         and Europe [syn: broom tree, needle furze, petty
         whin, Genista anglica]