Gehenna was just a garbage pit outside of Jerusalem where things were destroyed.
So, Gehenna is a fitting word for: destruction.
ALL the wicked will be ' destroyed forever ' - Psalms 92:7; Psalms 104:35; Proverbs 2:21-22; Psalms 37:10-11.
Sinner Satan will be destroyed by Jesus according to Hebrews 2:14 B,
When King James translated the word Gehenna into English as hell fire that put the flames in the grave.
No flames in the grave - just ' sleep ' as Jesus and the OT both teach.
- Psalms 6:5; Psalms 13:3; Psalms 1115:17; Isaiah 38:18; Ecclesiastes 9:5; John 11:11-14
Yes it was a place of rubbish, but before that it has another association with a certain place.
This is that the New International Dictionary of the Bible. J. D. Douglas, Merrill C. Tenney, said about Gehenna.
"Gehena
(geenna), a translation of the Aramaic from Hebrew.
(ge-ben-hinnom valley of the son of Hinnom). In the OT it was refered to as the Valley of Ben Hinnom (NIV) or the Valley of the sons Hinnom (KJV,RSV, ASV).
A valley west and SW of Jerusalem that formed part of the border between Judah and Benjamin (Joshua 15.8, 18.16), it was still recognized as the border after the Exile (Nehemiah 11.30-31) and is modern Wadi er-Rababi.
Here Ahaz (2Kings 16.3) (2Chronicles 28.3) and Manasseh (2Kings 21.6) (2Chronicles 33.6) sacrificed their sons to Molech (Jeremiah 32.35). For this reason Josiah defiled the place (2Kings 23.10).
After referring to these idolatrous practices (Jeremiah 7.31-32), Jeremiah prophesied a great slaughter of the people there and in Jerusalem (Jeremiah 19.1-13).
After the OT period, Jewish apocalyptic writes began to call the Valley of Hinnom the entrance to Hell, later Hell itself. In Jewish usage of the first century A.D, Gehenna referred to the intermediate state of the godless dead, but there is no trace this sense in the NT. The NT distinguishes sharply between Hades, the intermediate, bodiless state, and Gehenna, the state of final punishment after the resurrection of the body.
Gehenna existed before the judgment (Matthew 25.41). The word occurs 12 times in the NT, always translated "Hell" (ASV, RSV margin "Gehenna").
11 times it is on the lips of Jesus: as the final punishment for calling one's brother a fool (Matthew 5.22); for adultery, when the severest measures have not been taken to prevent commission of this offense (Matthew 5.29-30); in a warning about whom to fear (Matthew 10.28) (Luke 12.5); and (Matthew 18.9) (Mark 9.43, 45,47).
A hypocrite is called a "son of Hell" (Matthew 23.15) who cannot escape "being condemned to Hell" (Matthew 23.33). James 3.6 speaks of the "tongue" as "a fire...set on fire by Hell."
A fire was kept burning in the Valley of Hinnom to consume the garbage deposited there by the residents of Jerusalem. Terms parallel to Gehenna include "fiery furnace" Matthew 13.42,50), "fiery lake (Revelation 19.20; 20.14-15), "lake of burning sulfur" (Revelation 20.10), "eternal fire" Jude 7); "Hell" (2Peter 2.4), where the Greek phrase "sent... to Hell" means "cast down to Tartarus," a Greek name for the place of punishment of the wicked dead.
Its use by our Savior Jesus Christ warns us of the destiny that even the love of GOD does not avert from those who finally refuse His forgiveness.
See also Hades; Hell. ER (in the same Dictionary).
The New International Dictionary of the Bible. J. D. Douglas, Merrill C. Tenney.