When forming the plural of Italian nouns, the vowel endings change to indicate a change in number. For regular masculine nouns that end in -o, the ending changes to -i in the plural.
The table below includes a few nouns to start with:
PLURAL FORMS OF ITALIAN MASCULINE NOUNS ENDING IN -O
SINGULAR
PLURAL
ENGLISH
fratello
fratelli
brothers
libro
libri
books
nonno
nonni
grandfather
ragazzo
ragazzi
boys
vino
vini
wine
Regular feminine nouns that end in -a take on -e endings in the plural.
PLURAL FORMS OF ITALIAN FEMININE NOUNS ENDING IN -A
SINGULAR
PLURAL
ENGLISH
casa
case
houses
penna
penne
pens
pizza
pizze
pizzas
ragazza
ragazze
girls
sorella
sorelle
sisters
When forming the plural of nouns ending in a consonant, such as words of foreign origin, only the article changes: il film/i film; la photo/le photo. Here are some exceptions to the rule for forming feminine plurals:
- Feminine-noun ending -ea changes to -ee in the plural. For example: dea/dee (goddess/goddesses).
- Feminine-noun ending -ca changes to -che in the plural. For example: amica/amiche (friend/friends). Remember that -che is pronounced as "keh" in Italian.
Finally, be aware that some nouns end in -e. The plural forms of these nouns will end in -i (regardless of whether these nouns are masculine or feminine).
PLURAL FORMS OF ITALIAN NOUNS ENDING IN -E
SINGULAR
PLURAL
ENGLISH
bicchiere
bicchieri
(wine) glass
chiave
chiavi
keys
fiume
fiumi
rivers
frase
frasi
phrases
padre
padri
fathers
From:https://www.dbfei.com/Article/yidaliyu/201311/7727.html