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Nouns
There are two principal parts for Latin nouns: the nominative singular and the genitive singular. Each declension can be unequivocally identified by the ending of the genitive singular (-ae, -i, -is, -ūs, -ei). The stem of the noun can be identified by the form of the genitive singular as well.

There are five declensions for Latin nouns:

First declension (a stems, -ae genitive)
Mostly feminine. There is a small class of masculine exceptions generally referring to occupations.

The predominant letter in the ending forms of this declension is a. The nominative singular form consists of the stem and the ending -a, and the genitive singular form is the stem plus -ae.

Second declension (o stems, -ī genitive)
Mostly masculine nouns and neuter nouns. There are several small groups of feminine exceptions, including names of gemstones, plants, trees, and some towns and cities.

In the nominative singular, most masculine nouns consist of the stem and the ending -us, although some end in -er, which is not necessarily attached to the complete stem. Neuter nouns generally have a nominative singular consisting of the stem and the ending -um. However, every second-declension noun has the ending -ī attached as a suffix to the root of the noun in the genitive singular form. The predominant letter in the ending forms of this declension is o.

Second-declension -ius and -ium nouns
Nouns ending in -ius and -ium have a genitive singular in -ī in earlier Latin, which was regularized to -iī in the later language. Masculine nouns in -ius have a vocative singular in -ī at all stages. These forms in -ī are stressed on the same syllable as the nominative singular, sometimes in violation of the usual Latin stress rule.

There is no contraction of -iī(s) in plural forms and in the locative. In the older language, nouns ending with -vus, -quus and -vum take o rather than u in the nominative and accusative singular. For example, ('slave') could be servos, accusative servom.

Second-declension -r nouns
Some masculine nouns of the second declension end in -er or -ir in the nominative singular. The declension of these nouns is identical to that of the regular second declension, except for the lack of suffix in the nominative and vocative singular.

Some (but not all) nouns in -er drop the e genitive and other cases. For example, ('father-in-law') keeps its e. However, the noun ('(school)master') drops its e in the genitive singular.

For declension tables of second-declension nouns, see the corresponding Wiktionary appendix. The vocative puere is found but only in Plautus. The genitive plural virum is found in poetry.

Third declension
The third declension is the largest group of nouns. The nominative singular of these nouns may end in -a, -e, -ī, -ō, -y, -c, -l, -n, -r, -s, -t, or -x. This group of nouns includes masculine, neuter, and feminine nouns.

Consonant stems
The stem of a consonant-stem noun may be found from the genitive case by removing the ending -is. For example, the stem of f. 'peace' is pāc-, the stem of  n. 'river' is flūmin-, and the stem of  m. 'flower' is flōr-.

Masculine, feminine and neuter nouns often have their own special nominative singular endings. For instance, many masculine nouns end in -or (, 'love'). Many feminine nouns end in -īx (, 'phoenix'), and many neuter nouns end in -us with an r stem in the oblique cases ( 'burden'; 'time').

Fourth declension (u stems)
The fourth declension is a group of nouns consisting of mostly masculine words such as m. ('wave') and  m. ('port') with a few feminine exceptions, including  f. ('hand') and  f. ('house'). The fourth declension also includes several neuter nouns including n. ('knee'). Each noun has the ending -ūs as a suffix attached to the root of the noun in the genitive singular form. The predominant letter in the ending forms of this declension is u, but the declension is otherwise very similar to the third-declension i stems.

Fifth declension (e stems)
The fifth declension is a small group of nouns consisting of mostly feminine nouns like f. ('affair, matter, thing') and diēs, diēī m. ('day'; but f. in names of days). Each noun has either the ending -ēī or -eī as a suffix attached to the root of the noun in the genitive singular form. Nouns ending in -iēs have long ēī in the dative and genitive, while nouns ending in a consonant + -ēs have short eī in these cases.

The locative ending of the fifth declension was -ē (singular only), identical to the ablative singular, as in ('today').