Dictionary of Medieval Names
from European Sources

Thaddeus m. Aramaic תדי '(courageous) heart'.

The name of one of the twelve Apostles. Wycliffite Bible (1395): Tadee.

Italy
Latin
1243 Tadeum (acc) hennes-vol1 110; 1285 Tadei (gen) Perugia1285 p. 156; 1366 Taddei (gen) Livi 63; 1370 Taddei (gen) ibid. 23; 1478 Taddeo (abl) RCCaetani6 2720, Tadeus (nom) ibid. 2720; 1490 Tadey (gen) VitAs2 I; 1514 Thadeus (nom) SSPI p. 274
Italian
1429–1430 Tadeo DiaryLMA p. 269; 1513x1521 Thadeo LeoX p. 14
Cite as: S.L. Uckelman. "Thaddeus". In S.L. Uckelman, ed. The Dictionary of Medieval Names from European Sources, Edition 2017, no. 1. http://dmnes.org/2017/1/name/Thaddeus.