Ad. weak-noun grammar.
Polysyllabic nouns whose last syllable has a long vowel or diphthong are considered weak nouns. Monosyllabic nouns are also considered weak regardless of vowel length, though all attested monosyllabic nouns have a long vowel or diphthong (SD/425, 431). Weak nouns use suffixes when declined into the various noun cases (SD/425, 430). Weak nouns could be further subdivided into two groups (SD/437-8), those ending in a single consonant preceded by a long vowel or diphthong (Weak I) and those ending in a long vowel or diphthong preceded by one or more consonants (Weak II), for example: akhâs “chasm” (Weak I), pâ “hand” (Weak II).
Tolkien labeled these groubs Weak (a) and Weak (b), but the discussions here uses Weak I and Weak II for consistency with the subgroups Strong I and Strong II of strong-nouns. The majority of Weak II nouns were masculine and feminine, since these nouns often ended in long -ê, -î (feminine) or -ô, -û (masculine). Tolkien did not explicitly describe the full set of declensions of neuter Weak II nouns, but they can be deduced from other examples.
Weak I nouns add an inflectional suffix to their final consonant, whereas Weak II nouns add them to their final long vowel, often forming diphthongs. The few Weak II neuter-nouns must all end in -â, since neuter nouns cannot end in any other long vowel. The Weak I declensions below are derived from the chart on SD/430-1, while the Weak II declensions are mostly speculative.
The full set of declensions is:
|Case||Weak I||Weak II (-â)|
 The only attested declension for Weak II neuter nouns is the plural (SD/426). The others can be deduced from the suffixes of the Weak I noun declensions and the rules for Adûnaic vowel-combinations. These speculative declensions are marked with an asterisk (*) in the table above.
 The subjective singular of a neuter Weak II noun would, according to the rules of Adûnaic vowel-combination, have the same form as the normal singular, since the subjective suffix -a would be absorbed into the final -â of the noun.
 According to Tolkien, Weak I nouns with an â as their last vowel could sometimes have a strong plural by changing this vowel to î: akhâs → akhîs (SD/435, note 16). This was especially true in older texts. It seems that such formations were archaic by the time of Classical Adûnaic, but were sometimes used poetically, as plural batîn “roads” ← batân in the Lament of Akallabêth (SD/247).
The gendered-nouns are often weak, since they frequently have a long vowel in their final syllable (SD/436). In particular, the Weak II class consists mostly of gendered nouns. Weak gendered nouns are declined mostly like their neuter counterparts, differing only in the subjective and (for feminine nouns) sometimes in the objective and the plural.
Gendered nouns can end in any long vowel, not just â, so there are many more possible vowel combinations when case suffixes are added. The full set of declensions appear in the charts on SD/438. Most of the apparent complexity is actually the result of the standard rules of Adûnaic vowel-combinations:
|Case||Weak I||Weak II (-â)||Weak II (-ê)||Weak II (-î)||Weak II (-ô)||Weak II (-û)|
|subjective||nuphâran ||*Adûnân ||Avalên ||karbîn ||attôn ||ârûn |
|objective||nuphâru ||*Adûnâu||Avalê 
|attô ||ârû |
|Dual||nuphârat||*Adûnât ||Avalêt 
|karbîyat ||attôt 
|Dual Subjective||nuphârât ||*Adûnât||Avalêt
|Plural||nuphârî||Adûnâi ||Avalê 
|attôi ||ârûwî |
|Plural Subjective||nuphârîm ||Adûnâim ||Avalêm 
|attôim ||ârûwîm |
Some notes which, unless otherwise specified, are derived from the declension charts on SD/438:
 Only the attested declensions for Weak II nouns ending in -â are the plural and subjective plural forms. The remaining declensions can be deduced from the suffixes of the Weak I noun declensions and the rules for Adûnaic vowel-combinations. These speculative declensions are marked with an asterisk (*) in the table above.
 The word karbî “mare” is the feminine form of karab “horse” (SD/434).
 As noted above, gendered Weak I nouns use the appropriate gendered subjective suffix: -an (common), -in (feminine) and -un: kathuphazgân “conqueror” (masculine) → kathuphazgânun (SD/429), banâth “wife” (feminine) → banâthin (SD/437). The subjective suffix can also be used to indicate the gender of an otherwise common noun: nûph “fool” → nûphan (unspecified), nûphin (feminine), nûphun (masculine) (SD/438).
 Gendered Weak II nouns reduce the subjective suffix to -n in all cases.
 In Classical Adûnaic, feminine nouns often replace the usual objective inflection -u- with the vowel i instead (SD/432). For Weak I nouns, the result is: mîth “baby girl” → (objective) mîthi instead of mîthu.
 The feminine objective inflection -i- is absorbed into Weak II nouns ending in -ê and -î, so that the objective and normal singular forms are identical in such cases. Archaically, the objective was formed with the general objective suffix -u and a glide-consonant y: -ê → †-ayu (or -âyu?) and -î → †-îyu.
 The objective inflection -u- is absorbed into masculine Weak II nouns ending in -ô and -û, so that the objective and normal singular forms are identical in such cases. Unlike the feminine Weak II nouns, there was no archaic glide-consonant form, since the primitive suffixal ✶-u was the same as the final vowel of the primitive endings ✶-au or ✶-ū and was thus absorbed even archaically.
 For duals of Weak II nouns ending in -â, -ê or -ô, the vowel of the dual suffix -at is absorbed, leaving only -t. Archaically, however, the final -ê and -ô instead decomposed into †-ay and †-aw before the dual -at, as discussed in the entry on the glide-consonant.
 For subjective duals, wherever the normal dual form has a short a, it is lengthened to long â in the subjective case via the usual a-fortification process.
 For plurals of Weak II nouns ending in -â, -ô or -û, the plural inflection -î- either forms a long diphthong (with â, ô) or is separated from the final vowel (with û) by the usual glide-consonant w. This is entirely consistent with the standard rules for Adûnaic vowel-combinations.
 For plurals of Weak II nouns ending in -ê or -î (which were feminine), the plural inflection -î- is absorbed according to the standard rules for Adûnaic vowel-combinations, so that the normal singular and plural forms are identical: izrê “sweetheart” (singular) and izrê “sweethearts” (plural) (SD/438). Sometimes, though, a linking-consonant n is inserted between the final vowel and the plural suffix -î, to distinguish the singular and plural forms: izrênî “sweethearts” (plural) (SD/438). In the examples given by Tolkien, this only happened with nouns ending in -ê, but the process may have applied to nouns ending in -î as well.
 For all gendered weak nouns, the gendered subjective plural suffix -im is added to the plural form. In all cases, the vowel i of the suffix is absorbed according to the standard rules for Adûnaic vowel-combinations, leaving only -m.
|Examples (weak-I neut)|
|abâr||“strength, endurance, fidelity”|
|batân||“road, path, way”|
|bêth||“expression, saying, word”|
|rôth||“foam, white crest of waves”|
|Examples (weak-II neut)|
|Nimriyê||“Nimrian Tongue, *Elvish”|
|Examples (weak-I gendered)|
|mîth||“baby girl, maid-child, little girl”|
|phazân||“prince, king’s son”|
|sapthân||“wise man, wizard”|
|Examples (weak-II gendered)|
|#Adûnâ||“Númenórean, (lit.) Westerner”|
References ✧ SD/425, 430-431, 437-438