Concise Bible Dictionary:
One of the twelve apostles, who is not referred to by name except in the lists of the twelve (Matt. 10:3; Mark 3:18; Luke 6:14; Acts 1:13). Probably identical with Nathanael: (Compare John 1:45; John 21:2).
Potts’ Bible Proper Names:
Son of Tholomacus, or Talmai; a furrow; that suspends the water:― a Christian apostle [NATHANAEL], Matt. 10:3. {Filius Thalomaci; sulcus}