Adûnaic nouns end in either a vowel or a single consonant, since clusters were not allowed as final-consonants in Adûnaic (SD/426). In cases where the noun was originally produced by a suffix, it is limited to the final consonants used in suffixion. In cases where the noun is “basic”, that is derived directly from a primitive biconsonantal- or triconsonantal-root such as PUH or PHARAZ, it can end in any consonant.

Tolkien indicated that such basic noun forms are uncommon except in neuter-nouns, though they are quite common in neuters (SD/426). Basic nouns are particularly rare for feminine-nouns, the only commonly-used example being nithil “girl” (SD/426-7). Such basic nouns are generally the only way an Adûnaic noun can end in a consonant without suffixion.

Primitive Adûnaic nouns always had at least two consonants (SD/416). Classical Adûnaic nouns that seem to be exceptions to this rule have all undergone some kind of consonant loss from its primitive form, either because a primitive consonant vanished, as with Êru “God” < √ʔIR (SD/432), or because a primitive consonant became a vowel, as with pâ “hand” < ✶paʒa and khô “crow” < khau < ✶khaw (SD/426).