Tolkien’s invented language for the people of Númenor was Adûnaic. It was the native language of the Númenóreans, also called the Dúnedain, and is presented as a language descended from the speech of Men who lived on the island kingdom.
Adûnaic appears most substantially in Tolkien’s notes about the history of Númenor and in the account known as The Notion Club Papers. The language’s grammar and vocabulary were not developed as fully as those of Quenya or Sindarin, but Tolkien still gave it a place in the historical evolution of Middle-earth’s languages.
Readers may confuse Adûnaic with Westron, the Common Speech used widely during the events of The Lord of the Rings. Westron developed from Númenórean linguistic traditions, but it is not the same language. Quenya and Sindarin, meanwhile, are major Elvish languages.