-s or -es
Add -s to form the plural of most nouns.
table, tables
paper, papers
Add -es to singular nouns ending in -s, -sh, -ch, and -x.
church, churches
dish, dishes
Ordinarily add -s to nouns ending in -o when the -o is preceded by a vowel.
radio, radios
video, videos
Add -es to nouns ending in -o when the -o is preceded by a consonant.
hero, heroes
tomato, tomatoes
Plurals of hyphenated compound words
To form the plural of a hyphenated compound word, add -s to the chief word even if it does not appear at the end.
mother-in-law, mothers-in-law
Plurals of non-English words
English words derived from other languages such as Latin or French sometimes form the plural as they would in their original language.
medium, media
chateau, chateaux
criterion, criteria
Related topic:
Pluralizing numbers, letters, abbreviations, and words mentioned as words