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
    n 1: (New Testament) supposed brother of St. James; one of the
         Apostles who is invoked in prayer when a situation seems
         hopeless [syn: Jude, Saint Jude, St. Jude, Judas,
         Thaddaeus]
    2: (New Testament) the Apostle who betrayed Jesus to his enemies
       for 30 pieces of silver [syn: Judas, Judas Iscariot]
    3: someone who betrays under the guise of friendship
    4: a one-way peephole in a door