First declension

In the Latin language, declension refers to the method of inflecting nouns and adjectives to produce the 6 grammatical cases: nominative, genitive, dative, accusative, ablative and vocative. The first declension in most cases applies to nouns and adjectives that end in -a. Nouns that are declined this way will be referred to as nouns of the first declension. They are of feminine gender most of the time, except when they refer to occupations when they are masculine. Words of masculine gender that decline according to the first declension are always nouns.

Not all nouns of the first declension end in -a. Words that stem from the Greek language and end in -e, -es and even -as are also declined using most case endings for words ending in -a. These nouns can be feminine and masculine. These words are also always nouns.

Declension of words ending in -a
For example, let's look at the noun flamma (flame, fire).

Declension of words ending in -e, -es or -as
The plural forms of these nouns are declined identically as words ending in -a. There are differences in the singular forms.

The only declension difference between -e and -es ending nouns is in the singular genitive case.

The only declension difference between -es and -as ending nouns is in the singular accusative and ablative cases. Simply put, all "e"s are switched to "a"s.

Notice that the declension of nouns ending in -es is quite similar to the declension of the most common nouns of the first declension which, similarly, end in -a.