A genitive relationship between nouns is one that expresses possession or other close relationship. In English, the genitive can be expressed with an apostrophe-s (’s) or the preposition “of”, such as “the king of Númenor” or “Númenor’s king”. English can also form a genitive relationship between nouns simply by putting the modifying noun in front of the noun it modifies: “soldier king” would mean “a soldier-like king”. The different ways of forming the genitive can have subtle differences in meaning: “soldier’s king”, “soldier king”, and “king of soldiers” have different connotations, each describing different kinds of genitive relationships: possessive-genitive, adjectival-genitive, composition-genitive, and so forth.

Like English, Adûnaic has several ways of expressing genitive relationships (SD/428-9, 435). It can put the modifying noun before the noun it modifies: kadar-lâi “city-folk”, Anadûnê-ârû “Númenor-king”. It can also use the genitive prefix an- “of”. The modifying noun receives this prefix, and the resulting phrase is placed after the noun it modifies: ârû an-Anadûnê “king of Númenor”. Frequently the genitive prefix is elided so that the vowel a is lost: ârû ’nAnadûnê “king of Númenor” (SD/429). This happens, for example, when the preceding noun ends in a vowel.

In many situations, the two ways of forming the Adûnaic genitive are interchangeable, in much the same way that English can use either apostrophe-s (’s) or “of”. Where the modifying noun is plural, however, the genitive prefix an- must be used, as in ârû ’nAdûnâi “king of the Númenóreans”. A construction like **Adûnâi-ârû “Númenóreans-king” is not possible, since a plural noun in this position has considered to be in an objective relationship with the following noun. Tolkien described it thus (SD/429):

Such object-constructions with plural nouns are rare. Adûnaic generally uses a singular noun in the objective, with the plurality understood: Balkumagân “Ship-builder” and Nimruzîr “Elf-friend” instead of **Balîkmagân “Ships-builder” and **Nimîrzîr “Elves-friend”. This is similar to most such English constructions.

Also like English, Adûnaic could put two nouns in apposition, as two words or titles describing the same thing: Gimilzôr Ârû “Gimilzor the king” or Pharazôn kathuphazgân “Pharazôn the conqueror”. This appositional usage can be distinguished from genitive relationships by stress and tone (SD/428).

In writing, a genitive noun was connected to the noun it modified with a dash (-), whereas in speech the genitive noun had greater stress and higher tone (SD/435): compare Gimilzôr-Ârû “Gimilzor’s king” (stress on Gimilzor) versus Gimilzôr Ârû “Gimilzor the king” (stress on Ârû). Such genitive constructions often became actual compounds: Amatthâni = Amân + thâni = “Aman’s Land, Land of Aman”.