Strong's numbers
ταρταρόω (G5020)
tartaróō
tar-tar-o'-o
from (the deepest abyss of Hades); to incarcerate in eternal torment:--cast down to hell.
Abbott–Smith
*† ταρταρόω, -ῶ (< Τάρταρος, a Greek name for the underworld, esp. the abode of the damned),
to cast into hell: II Pe 2:4 (v. Mayor, in l.).†
From G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922), in the public domain.
1 occurrence
Shown in the King James Version (KJV), whichever translation you read in — it is the text these numbers are tagged against.
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2 Peter 2:4
For if God spared not the angels that sinned, but cast them down to hell, and delivered them into chains of darkness, to be reserved unto judgment;