Tartarus — A Greek word, not found in the Hebrew, used by Peter in 2 Peter 2:4 when referring to the angels (sons of god) who were cast down to hell (Tartarus) at the time of Noah's flood.
Used twice in the Septuagint, the Greek translation of the Old Testament. First time was when translating the word "field" or "plain" where the living creatures play (or mock) in Job 40:20 in a reference to Behemoth (great monster of the land).
Second time was translating the word "deep" (Tehowm in Hebrew, Tartarus in Greek) in Job 41:31-34, verse 32 in a reference to Leviathan (great monster of the sea). "31: He makes the depths to boil like a pot, he makes the sea like a pot of ointment. 32: He makes a path to shine after him, one would think the deep to be hoary (grey-haired). 33: Upon earth there is not his like, one made without fear. 34: He beholds every high thing, He is king over all the children of pride."
Click here for the Septuagint version, which translates "hoary" as "a captive".