a sunless abyss, below Hades, in which Zeus imprisoned the Titans.
2.
a place in Hades for the punishment of the wicked.
British Dictionary definitions for Tartarus
Tartarus
/ˈtɑːtərəs/
noun (Greek myth)
1.
an abyss under Hades where the Titans were imprisoned
2.
a part of Hades reserved for evildoers
3.
the underworld; Hades
4.
a primordial god who became the father of the monster Typhon
Word Origin
C16: from Latin, from Greek Tartaros, of obscure origin
Word Origin and History for Tartarus
n.
the abyss below Hades in Greek mythology, from Greek Tartaros, of uncertain origin; "prob. a word of imitative origin, suggestive of something frightful" [Klein].