Fausset's Bible Dictionary
JUDE LEBBAEUS, THADDAEUS. Jude calls himself "servant of Jesus Christ, and brother of James", namely, the apostle James "the Lord's brother" (a title which James omits in humility, as he was strictly only cousin of Christ), bishop of Jerusalem (compare Gal_1:19). (See JAMES.) Similarly Jude was both an apostle and brother of our Lord. All Christ's brethren were not apostles, only James and Jude, sons of Alphaeus or Clopas and Mary. James being better known, Jude designates himself "brother of James." Like Paul in epistles to Philippians, Thessalonians, and Philemon, Jude omits his apostleship. A forger would have been sure to head the epistle with the designation "apostle."
Jude is distinguished from Judas Iscariot by the names Lebbaeus and Thaddaeus, i.e. courageous, from Hebrew leeb "heart," thad "breast," or hodah "praise" (Adai is the name in Syriac): Mat_10:3; Mar_3:18. Luke and John writing later, when no confusion with Judas Iscariot was likely, call him "Judas." The only notice of him is in Joh_14:22, where, not understanding Jesus' promise (Joh_14:21), Judas (not Iscariot) asked "Lord, how is it that Thou wilt manifest Thyself unto us and not unto the world?" His position in the last group of four among the twelve implies, like his question, low views at that time of the spirituality of Messiah's kingdom.
Eusebius tells that Abgarus, king of Edessa, being sick sent begging Jesus to come and heal him; the Lord replied, praising his faith because, though he had not seen, he believed, and promising when He should ascend to send one of His disciples to heal and give him life. Thomas then was inspired to send Thaddaeus. Such a message may have been sent verbally, and its substance afterward written (compare Mat_15:22; 2 Kings 5). Hegesippus (Eusebius, E. H. iii. 20) states that when the emperor Domitian inquired after David's posterity, grandsons of Jude "the Lord's brother" were brought before him; they stated their possessions were 39 acres, and that they paid him taxes thereout and lived by labour, pointing as a proof to their hard hands. They added, Christ's kingdom is not of this world, but heavenly, and will be manifested when He shall come again in glory.
Mar_3:18. Same as Lebbaeus or Judas not Iscariot (Joh_14:22). (See JUDE.) The Sinaiticus and Vaticanus manuscripts read in Mat_10:3 only "Thaddaeus, "omitting "and Lebbaeus whose surname was."
Taken from: Fausset's Bible Dictionary by Andrew Robert Fausset (1821-1910)