Thaddius \th(ad)-dius\ as a boy's name is a variant of Thaddeus (Aramaic), and the meaning of Thaddius is "heart".

The baby name Thaddius sounds like Thaddaus, Thadeus, Thaddaeus, Thaddaos and Thaddaios. Other similar baby names are Caddis, Caddiss and Gaddis.