'Hinnom' definitions:

Definition of 'Hinnom'

Hinnom a deep, narrow ravine separating Mount Zion from the so-called "Hill of Evil Counsel." It took its name from "some ancient hero, the son of Hinnom." It is first mentioned in Josh. 15:8. It had been the place where the idolatrous Jews burned their children alive to Moloch and Baal. A particular part of the valley was called Tophet, or the "fire-stove," where the children were burned. After the Exile, in order to show their abhorrence of the locality, the Jews made this valley the receptacle of the offal of the city, for the destruction of which a fire was, as is supposed, kept constantly burning there.
The Jews associated with this valley these two ideas, (1) that of the sufferings of the victims that had there been sacrificed; and (2) that of filth and corruption. It became thus to the popular mind a symbol of the abode of the wicked hereafter. It came to signify hell as the place of the wicked. "It might be shown by infinite examples that the Jews expressed hell, or the place of the damned, by this word. The word Gehenna [the Greek contraction of Hinnom] was never used in the time of Christ in any other sense than to denote the place of future punishment." About this fact there can be no question. In this sense the word is used eleven times in our Lord's discourses (Matt. 23:33; Luke 12:5; Matt. 5:22, etc.).

Hinnom, there they are; their riches