WordNet (r) 3.0 (2006):

Thaddaeus
    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]

Easton's 1897 Bible Dictionary:

Thaddaeus
   breast, the name of one of the apostles (Mark 3:18), called
   "Lebbaeus" in Matt. 10:3, and in Luke 6:16, "Judas the brother
   of James;" while John (14:22), probably referring to the same
   person, speaks of "Judas, not Iscariot." These different names
   all designate the same person, viz., Jude or Judas, the author
   of the epistle.