Nouns are found in the singular or plural form..
Most words merely take on the ‘s’ to form a plural, eg:
house – houses
cat – cats
bedroom – bedrooms
However, there are some exceptions, nouns that end with -ch, -x, -s, -sh add ‘-es’ to the end of the word, eg:
church – churches
box – boxes
dish – dishes
If the noun ends in a vowel + y, add an ‘-s’
holiday – holidays
monkey – monkeys
guy – guys
When the noun ends in a consonant + y, drop the y and replace it with ‘-ies’
sky – skies
baby – babies
party – parties
If the noun ends in a ‘f’ or ‘fe’, drop the ‘y’ and replace it with ‘-ves’
wolf – wolves
half – halves
loaf – loaves
When the noun ends with an ‘o’, then add ‘-es’
hero – heroes
zero – zeroes
volcano – volcanoes
However, there are some words ending in ‘o’ that simply take on an ‘-s’
piano – pianos
photo – photos
radio – radios
Some of the nouns ending with ‘oo’, just simply add on ‘-s’
zoo – zoos
igloo – igloos
Most nouns ending in ‘is’, drop the ‘is’ and add ‘-es’
crisis – crises
oasis – oases
When the noun ends in ‘us’, you can either add an ‘-es’ or drop the ‘us’ and add an ‘-i’
hippopotamus – hippopotamuses / hippopotami
syllabus – syllabuses / syllabi
octopus – octopuses / octupi
There are some nouns that keep the form in singular and plural, usually names of animals, but not limited to.
fish
sheep
deer
moose
aircraft
series
Some nouns keep their singular form as they are ‘uncountable’
baggage
information
gold
advice
weather
Here are some nouns that appear only in plural form
scissors
clothes
trousers
savings
measels
goods
tweezers
glasses (reading)
And these nouns actually change in the plural form
tooth – teeth
foot – feet
mouse – mice
person – people
child – children
In compound nouns, the last word normally take on the plural form
travel-agent – travel-agents
boy-friend – boy-friends
break-in – break-ins
When the noun contains a preposition, the noun before the preposition takes on the plural form
son-in-law – sons-in-law
runner-up – runners-up
passer-by – passers-by