Nouns in Italian

In Italian, nouns can be masculine or feminine.
As a rule, masculine nouns have the "-o" ending:

quaderno – copybook
cavallo – horse
Feminine nouns have the "" ending:

bambina – girl
matita – pencil
However, there are exceptions: words that are feminine, but have the "-o" ending:

radio – radio
metro – metro
There is a concept of a "general" gender in Italian.
It is used to refer to nouns that have the same form for both masculine and feminine and can be distinguished by the article.

For example:
il nipote – nephew (masculine gender)
la nipote – niece (feminine gender)
As a rule, the plural of Italian nouns is formed by changing the final vowel.
Thus, masculine nouns that have "-o" ending change it to "-i":
ragazzo – ragazzi – boys
tavolo – tavoli – tables

Feminine nouns that have "-a" ending change it to "-e":
bambina – bambine – girls
casa – case – houses
When the plural is formed, if a noun ends in "-co / go" or "-ca / ga" in the singular, the letter "h" appears before the final vowel:

casco (helmet) – caschi
lago (lake) – laghi
amica (girl friend) – amiche
lega (union) – leghe

The letter "h" is needed to keep the phonetic sound.
Remember: when plural nouns are formed, not only the final vowel but also the article changes:
il bambino – I bambini (children)
l'albero – GLI alberi (trees)
la scala – LE scale (stairs)
A number of Italian nouns do not form plurals according to the standard rules.
Some nouns have the same form in both the singular and the plural. Usually, these are the following:
Words in which the stress falls on the last syllable:

la città (city) – le città
il caffè (coffee) – i caffè
Words that end in a consonant:

il bus (bus) – i bus
il film (film) – i film

Monosyllabic nouns:

il ré (king) – i ré
la gru (crane) – le gru
Feminine nouns that have the "-o" ending
(as mentioned above):
la radio (radio) – le radio

Feminine nouns that have "-i" or "-ie" ending:
la crisi (crisis) – le crisi
la serie (series) – le serie

la moglie (wife) – le mogli
Nouns that do not follow the final vowel rule:

l'ala (wing) – le ali (wings)
l'arma (weapon) – le armi (weapons)

In such case, the ending "-i" appears in the plural instead of the expected ending "-a".
Masculine nouns (usually of Greek origin), in which there is "" instead of "-o" in the singular, that turns into "-i" in the plural

il problema (problem) – i problemi
il teorema (theorem) – i teoremi

Nouns that do not follow any rules when forming a plural:
In such words, additional syllables may appear:

l'uomo (man) – gli uomini
il bue (bull) – i buoi

Gender may change:

l'uovo (egg) – le uova
il dito (finger) – le dita
la mano (arm) – le mani
il ginocchiо (knee) – le ginocchia