THASSI thăs’ ī (Θασσί). The surname of Simon the Maccabee, one of the five sons of Mattathias (1 Macc 2:3). After securing independence for the Jews, he became the founder of the Maccabean dynasty. It is not certain what the name means; possibly it is zealous.

International Standard Bible Encyclopedia (1915)

The surname of Simon, the brother of Judas Maccabeus (1 Macc 2:3; Syriac "Tharsi"). It is uncertain what the name means, perhaps "director" or "guide," since Simon was "a man of counsel," or "the zealous."