The Greek term γέεννα is derived from a Hebrew phrase meaning ‘Valley of Hinnom,’ a ravine running along the south side of Jerusalem and a place where the rubbish from the city was constantly being burned. According to late Jewish popular belief, the last judgment was to take place in this valley, and hence the figurative extension of meaning from ‘Valley of Hinnom’ to ‘hell.’ In most languages γέεννα is rendered as ‘place of punishment’ or ‘place where the dead suffer’ or ‘place where the dead suffer because of their sins.’

(Louw, J. P., & Nida, E. A. (1996, c1989). Greek-English lexicon of the New Testament : Based on semantic domains (electronic ed. of the 2nd edition.) (1:5). New York: United Bible societies.)

Hell is the place of the future punishment call “Gehenna” or “Gehenna of fire”. This was originally the valley of Hinnom, south of Jerusalem, where the filth and dead animals of the city were cast out and burned; a fit symbol of the wicked and their future destruction.
(Strong, J. (1996). The exhaustive concordance of the Bible : Showing every word of the test of the common English version of the canonical books, and every occurence of each word in regular order. (electronic ed.) (G1067). Ontario: Woodside Bible Fellowship.)
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