Noun can be in singular or plural number. Singular shows only one person, animal, thing, etc. Plural shows more than one person, place, thing, etc.
Plural Forms:
A) Adding "S"
ant/ants
boy/boys
girl/girls
river/rivers
school/schools
B) Adding "ES" to nouns ending in "X/SH/S" (hissing sound)
box/boxes
fox/foxes
flash/flashes
branch/branches
dress/dresses
C) Adding "ES" to nouns endig in "O"
hero/heroes
tomato/tomatoes
buffalo/buffaloes
potato/potatoes
cargo/cargoes
* There are exceptions:
photo/photos
tattoo/tattoos
bamboo/bamboos
radio/radios
zoo/zoos
D) Changing "Y" to "IES"
lady/ladies
city/cities
story/stories
duty/duties
army/armies
*There are exceptions when "Y" is after a vowel (a,e,i,o,u)
day/days
joy/joys
toy/toys
guy/guys
key/keys
E) Changing "F/FE" to "VES"
calf/calves
leaf/leaves
life/lives
knife/knives
thief/thives
*There are exceptions:
roof/roofs
proof/proofs
cliff/cliffs
sheriff/sheriffs
F) Changing the inside vowel
man/men
woman/women
goose/geese
tooth/teeth
foot/feet
G) Changing part of word
mouse/mice
louse/lice
emporium/emporia
bacterium/bacteria
cactus/cacti
H) Adding characters "EN/REN"
child/children
ox/oxen
I) Some nouns have no plural form
sheep
deer
furniture
music
advice
J) Some nouns are used only in plural form
pants
shorts
pyjamas
scissors
spectacles
K) Compound nouns
son-in-law/sons-in-law
looker-on/lookers-on
passer-by/passers-by
commander-in-chief/commanders-in-chief
Lord Justice/Lords Justice
L) Foreign words
abascus/abaci
bacillus/bacili
oasis/oases
beau/beaux
basis/bases