Adûnaic (so spelled in The Lord of the Rings, but in some earlier writings appearing as Adunaic) was the native language of the Númenórean people (LotR/1129). Many Númenóreans also spoke the Elvish tongues Sindarin and Quenya, the former being common in ordinary speech, the latter only in ritual, scholarship and in the names of great places and nobility (LotR/1128). The Elvish tongues fell out of favor when the Númenóreans were alienated from the Elves of Valinor, and thereafter Adûnaic became the dominant language of Númenor (though Elvish languages were still spoken in secret by the Faithful).

Númenor was destroyed when Ar-Pharazôn tried to invade Valinor, and the Classical Adûnaic language perished with it. Though Adûnaic was still spoken in the surviving Númenórean colonies, many of them were dominated by the Faithful who had little incentive to preserve the language. This Exilic Adûnaic blended with the native languages of Northeastern Middle-earth, becoming Westron. It may have survived longer in the Black Númenórean colonies allied with Sauron, most notably Umbar, but even there it was probably blended with or replaced by the native languages of the Haradrim. It was a dead language by the time of the War of the Ring.

Adûnaic (or Adunaic) is an Anglicanized form of the language’s name. The actual term is Adûnayân.