Adunaic was the language spoken by the men of Númenor during the Second Age in J.R.R. Tolkien
's mythos. It is the only "Mannish" tongue on which we have more information than guesses. The reason for this is that in the History of Middle Earth books, published after Tolkien's death and containing much of Tolkien
's draft material, is found a section called "Lowdham's Report" (Sauron Defeated: 413-440) Lowdham was a member of the Notion Club who learned Adunaic in his dreams. Lowdham's Report amounts to a grammar on the language -- indeed, Adunaic is the only one
of Tolkien's languages
for which we have a published grammar. However, the grammar is not complete and we have very little vocabulary which seriously limits our actual use of the Númenórean language.
Adunaic like Primitive Elvish, had a system of consonantal "word bases" (like the Semitic languages of today) with an associated vowel (differing from Khuzdul, which only has the word bases) which must appear in every word derived from those bases. The Adunaic noun has four "genders", Masculine, Feminine, Neuter and Common. The Adunaic noun also has three cases: Nominative, Subjective and Objective.
To anyone interested in learning more about the language, Sauron Defeated and Helge Fauskanger's Adunaic article (http://www.uib.no/People/hnohf/adunaic.htm) are excellent places to go.