This word tartarus is used just 4 times in the entire Bible, including the Greek OT. One Hebrew equivalent, evinced by Proverbs 30:16 is Sheol. Get it? The Hebrew word sheol is used in place of tartarus in Proverbs 30:16; therefore, Sheol is a Greek equivalent of tartarus. Sheol is used more than 60 times in the OT. Sheol is usually translated as hades in the NT. Jesus has the keys to hades (Rev. 1:18).
The Online Bible numerical equivalents of these words are these
tartarus 5020:
Sheol 07585
hades 86
Thayer's lexicon has this to say about hades:
1) name Hades or Pluto, the god of the lower regions
2) Orcus, the nether world, the realm of the dead
3) later use of this word: the grave, death, hell
In Biblical Greek it is associated with Orcus, the infernal regions, a dark and dismal place in the very depths of the earth, the common receptacle of disembodied spirits. Usually Hades is just the abode of the wicked, Lu 16:23; Re 20:13,14; a very uncomfortable place. TDNT.