Quick answer
Thaddeus is a boy name meaning "heart, breast".
Pronunciation: English /ˈθæd.i.əs/; English /θæ.ˈdi.əs/.
Meaning and history
From Θαδδαῖος (Thaddaios), the Greek form of the Aramaic name תַדַּי (Ṯaddai). It is possibly derived from Aramaic תַּד (taḏ) meaning "heart, breast", but it may in fact be an Aramaic form of a Greek name such as Θεόδωρος (see Theodore ). In the Gospel of Matthew, Thaddaeus is listed as one of the twelve apostles, though elsewhere in the New Testament his name is omitted and Jude 's appears instead. It is likely that the two names refer to the same person.
Notes and context
Usage: english, biblical, biblical latin | Ancient Greek: Θαδδαῖος