Tadeus is of Polish origin, derived from the Teutonic name Thadeus, which means "courageous heart." It is a variant form of Theodore, meaning "gift of God," and shares its root with names like Matthew and Theodore. Tadeus is often associated with St. Jude Thaddeus, one of Jesus's apostles in the Bible. In the Middle Ages, Tadeus was popular among Polish nobility due to its biblical connections. Today, it remains a less common but distinctive name choice, offering a unique alternative to traditional names like Theodore or Matthew.
The name Tadeus experienced fluctuations in popularity over the years, with a peak of 7 births in 1918 and troughs of 5 births in 1917, 1920, and 1921. The overall total of 34 births over these years suggests that Tadeus was not an extremely common name but still saw some usage.