What does Thaddius mean?
Thaddius /thad-dius/ [3 sylls.] as a name for boys. Thaddius' name origin is Aramaic, and the name Thaddius means "heart". Thaddius is a version, with the suffix -ius, of Thaddeus (Aramaic): also possibly derives from Theodorus.
How popular is Thaddius?
Thaddius is an uncommon first name for men. Thaddius is an equivalently rare surname too for all people. (2000 U.S. Census)
Prominent varying forms of Thaddius (not ranked) are Tad, Thad and Thaddeus (#732 last year). Forms like Thaddaios are uncommon. Adoption of these boy names reached its most widespread during 1970-1979 (usage of 0.421%) and is now significantly lower (usage 0.0893%, 78.8% less), with the forms Tad, Thad and Thaddeus becoming less in vogue. Below is a graphed comparison of the usage of Thaddius and related names. (Top 1000 Birth Names Statistics, 2014)