Thaddaeus = "large hearted, courageous"
1) one of the twelve apostles. From a comparison with the catalogue of apostles in Luk 6:16, and Act 1:13, is seems that Judas, Lebbaeus and Thaddaeus were the same person, and the writer of the book of Jude.
Part of Speech: noun proper masculine
Of uncertain origin; Thaddaeus, one of the Apostles: - Thaddus.
These two sites give similar information, with the definition from several dictionaries and statistics on the use of the word.
Perseus Digital Library
University of Chicago's Logion lexicon
Thayer's dictionary plus other information.
From this site's dictionary (in Italian)
Click on the first column to search for that word as a form of the root Θαδδαῖος; click on the second column to search for that grammatical form of the root Θαδδαῖος; click on the third column to search for that word and grammatical form; click on the total to search for the root Θαδδαῖος.