Amon Amarth

The great volcano in the midst of the Plateau of Gorgoroth was most commonly known in Elvish as Orodruin, the Fire-mountain, but in the last years of the Second Age it acquired a new name among the Men of Gondor. In the year II 3429, their kingdom had been established for a little over a century, and Sauron had not been seen since the Downfall of Númenor. Orodruin had lain dormant for that time, but it now burst into new flame, and the Gondorians perceived that it meant the return of Sauron. Thus they gave the Fire-mountain a new Elvish name, Amon Amarth, meaning 'hill of doom', though almost universally translated as 'Mount Doom'.¹

Their concerns proved to be well founded, as Sauron immediately sent an army over Ephel Dúath and captured Minas Ithil. This was the beginning of the War of the Last Alliance, which would last for twelve years, and end with a hard-bought victory against Sauron.

It's unclear whether the name Amon Amarth continued in use after these events, but certainly the older Elvish name Orodruin remained much more common. In the tongues of Men, however, the translated form of Amon Amarth became widespread, so that the name for the mountain in the Common Tongue remained 'Mount Doom' throughout the Third Age.