Thaddeus \th(ad)-deus\ as a boy's name is pronounced THAD-ee-us. It is of Aramaic origin, and the meaning of Thaddeus is "heart". Also possibly derives from Theodorus, meaning "God's gift". Biblical: one of the 12 apostles. Jude is another form of the name.
Thaddeus has 15 variant forms: Tad, Tadd, Taddeo, Taddeusz, Tadeo, Tadio, Tadzio, Thad, Thaddaios, Thaddaos, Thaddaeus, Thaddaus, Thaddius, Thadeus and Thady.