The Collaborative International Dictionary of English v.0.48:

Tophet \To"phet\, n. [Heb. t[=o]phet, literally, a place to be
   spit upon, an abominable place, fr. t[=u]ph to spit out.]
   A place lying east or southeast of Jerusalem, in the valley
   of Hinnom. [Written also Topheth.]
   [1913 Webster]

         And he defiled Topheth, which is in the valley of the
         children of Hinnom.                      --2 Kings
                                                  xxiii. 10.
   [1913 Webster]

   Note: It seems to have been at first part of the royal
         garden, but it was afterwards defiled and polluted by
         the sacrifices of Baal and the fires of Moloch, and
         resounded with the cries of burning infants. At a later
         period, its altars and high places were thrown down,
         and all the filth of the city poured into it, until it
         became the abhorrence of Jerusalem, and, in symbol, the
         place where are wailing and gnashing of teeth.
         [1913 Webster]

               The pleasant valley of Hinnom, Tophet thence
               And black Gehenna called, the type of hell.
                                                  --Milton.
         [1913 Webster]