Adûnaic derived from the closely related Bëorian and Hadorian dialects of Taliska, the language spoken by the first and third houses of the Edain when they first entered Beleriand during the First Age (the language(s) of the second house, the Haladin, seems to have had little or no influence on Adûnaic whatsoever, despite the apparent presence of both the Haladin and the Drúedain in Númenor prior to its downfall). This language seems to have primarily been a creole of the Dwarfish Khuzdul and some Avarin dialects, and it is almost wholly unclear which parts (if any) of its vocabulary and structure were purely "Mannish" in origin, though the answer is probably very little (it is stated that Felagund was able to quickly master Taliska purely by determining the various changes undergone by its Avarin component from Primitive Quendian). Once the Edain settled in Beleriand, they eagerly learned Sindarin from its Grey Elven inhabitants, but retained their own tongue, probably whilst borrowing and adapting many Sindarin words to it. By the end of the First Age, Taliska had developed into a language that served as the basis for Adûnaic, the vernacular tongue of the Númenóreans, as well as the languages of the Rohirrim and the Men of Dale.
In Númenor, Adûnaic was the language used in day-to-day affairs by the majority of the population (though Sindarin was probably spoken by many). Its corpus, already a varied mixture of Khuzdul, Avarin, and Sindarin, was probably now exposed more heavily to the influence of Quenya (which served a role much the same as Latin in Medieval Europe) and possibly even Valarin, both due to regular contact with Aman. When the Númenóreans began to establish trading ports (later colonies) on the western shores of Middle Earth, Adûnaic mingled with the languages of various groups of Edain who had not travelled to Númenor, and the resulting trade language quickly spread throughout Eriador and its neighbours, laying the foundation for the later Common Speech.
Following the Akallabêth, the surviving Elendili who established the kingdoms of Arnor and Gondor shunned Adûnaic in favour of Sindarin due to the associations of the former with the tyrannical Ar-Pharazôn and his followers the King's Men. Neglected by the Faithful, Adûnaic (in various forms and dialects) remained the language of the common people throughout most of the west of Middle Earth, and by the time of the War of the Ring at the end of the Third Age, it had developed into the various dialects of Westron.
Although "classical" Adûnaic was not spoken after the Akallabêth, surviving groups of the King's Men (referred to as Black Númenóreans) who served and worshipped Sauron (notably in Umbar) continued to speak a debased form of the language (called Black Adûnaic) as recently as the War of the Ring at the end of the Third Age.
Very few words of Adûnaic are known, though those which are borrow heavily from various Elven languages. Adûnaic also seems to conform to a variant of the consonantal root system used in Khuzdul (as does its successor language, Westron). It is also one of perhaps only two or three of Tolkien's languages known to possess noun classes, which roughly correspond to four grammatical genders.