Adûnaic (‘The-Speech-of-the-West’) was the language adopted by the Dúnedain of Númenor during their days in power. Based largely on Mannish speech, it was the ancestral speech of the House of Hador; during the First Age, it was influenced by the Elvish tongue, as a result of Númenor’s ties with the Moriquendi and the Eldar. However, the language did not survive the Downfall of Númenor. The Faithful, those who had survived the Downfall, spoke either Sindarin or the Common Speech (which had itself been partly derived from ancient Adûnaic).
The names of all the Princes and Kings of Númenor (after Tar-Calmacil and excluding Tar-Palantír) were taken in Adûnaic, as was the name of Númenor’s Downfall itself, Akallabêth.