The Collaborative International Dictionary of English v.0.48:

Judas \Ju"das\, n.
   The disciple who betrayed Christ. Hence: A treacherous
   person; one who betrays under the semblance of friendship. --
   a. Treacherous; betraying.
   [1913 Webster]

   Judas hole, a peephole or secret opening for spying.

   Judas kiss,
   (a) a deceitful and treacherous kiss.
   (b) an act appearing to be an act of friendship, which is in
       fact harmful to the recipient.

   Judas tree (Bot.), a leguminous tree of the genus Cercis,
      with pretty, rose-colored flowers in clusters along the
      branches. Judas is said to have hanged himself on a tree
      of this genus (Cercis Siliquastrum). Cercis Canadensis
      and Cercis occidentalis are the American species, and
      are called also redbud.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Judas tree
    n 1: small tree of the eastern Mediterranean having abundant
         purplish-red flowers growing on old wood directly from
         stems and appearing before the leaves: widely cultivated in
         mild regions; wood valuable for veneers [syn: Judas tree,
         love tree, Circis siliquastrum]