In Italian, there are two types of invariable nouns: invariable by gender and invariable by number. When we say “by number,” we mean that they have the same form whether they are singular or plural.

Here are some examples:

Masculine nouns that end in -a:

• il sosia (i sosia), la sosia (le sosia) look-alike

Feminine nouns that end in -o:

• l’eco (f.) echo (the masculine version of the noun has two forms: l’eco, gli echi)

When the nouns have one syllabus, they are sometimes invariable:

• il re (i re) king

• lo sci (gli sci) ski (plural = un paio di sci / a pair of skis)

Feminine nouns that end in -ie (except for moglie, superficie, effigie):

• la calvizie baldness

• la serie series

• la progenie offspring

Some colors, when used as nouns, are also invariable and masculine:

• blu

• rosa

• viola

Truncated nouns are also invariable:

• la bici, le bici bicycle

• la moto, le moto motorcycle

Nouns that end in consonants are invariable:

• il film film, movie

• il bar cafè