The Collaborative International Dictionary of English v.0.48:

Thorny \Thorn"y\, a. [Compar. Thornier; superl. Thorniest.]
   [Cf. AS. [thorn]orniht.]
   1. Full of thorns or spines; rough with thorns; spiny; as, a
      thorny wood; a thorny tree; a thorny crown.
      [1913 Webster]

   2. Like a thorn or thorns; hence, figuratively, troublesome;
      vexatious; harassing; perplexing. "The thorny point of
      bare distress." --Shak.
      [1913 Webster]

            The steep and thorny way to heaven.   --Shak.
      [1913 Webster]

   Thorny rest-harrow (Bot.), rest-harrow.

   Thorny trefoil, a prickly plant of the genus Fagonia
      (Fagonia Cretica, etc.).
      [1913 Webster]

WordNet (r) 3.0 (2006):

thorny
    adj 1: bristling with perplexities; "the thorny question of
           states' rights"
    2: having or covered with protective barbs or quills or spines
       or thorns or setae etc.; "a horse with a short bristly mane";
       "bristly shrubs"; "burred fruits"; "setaceous whiskers" [syn:
       barbed, barbellate, briary, briery, bristled,
       bristly, burred, burry, prickly, setose,
       setaceous, spiny, thorny]