An adjective translated “western” formed from the noun adûni “the West” which was in turn formed from the adjective adûn “west”; the initial an- was the genitival prefix (SD/435). This adjective anadûni was in turn femininized to produce the place name Anadûnê “Westeresse, Númenor”.
anadûnêplace name. Westernesse
The Adûnaic name for Númenor (Q. Númenórë), with the same meaning as its Quenya name: “Westernesse” (S/261). In The Silmarillion appendix, Christopher Tolkien stated that is it a loan word from Elvish (SA/andúnë). According to J.R.R. Tolkien’s own writing (SD/426), this is true, albeit not directly. Anadûnê is a feminized form of the adjective anadûni “western, of the west”, which is itself related to S. dûn “west”.