Irregular noun plurals
In English, there are nouns that don’t follow the standard rules for pluralization. There are no easy ways to remember them, so they generally have to be memorized.
Most singular nouns form the plural by adding -s.
a sandwich — sandwiches
a rose — roses
There are also irregular noun plurals. The most common ones are listed in the table below.
man - menfoot - feetmouse - mice
woman - womentooth - teethlouse - lice
child - childrengoose - geeseox - oxen
There are nouns that are used only in the singular (eg. furniture, homework).
There are nouns that are used only in the plural (eg. clothes, people).
When one thing has two parts:
trousers, jeans, tights, shorts, pants, glasses, spectacles, pyjamas, scissors, scales.
To make them singular we use “a pair of”.
Those are nice jeans. That’s a nice pair of jeans.
In general we make the plural of a compound noun by adding -s to the "base word" (the most "significant" word).
a passer-by — passers-by
an apple tree — apple trees  
When a compound noun is with hyphens \((-)\), form the plural by adding -to the principal word in the compound.
mother-in-law — mothers-in-law
With compound nouns made of [noun \(+\) noun] the second noun takes an -s for plural.
The first noun acts like an adjective.
a tennis shoe — tennis shoes
If the first word of the compound is “man”/”woman”, both the words in the compound are used in the plural.
man-servant — men-servants
woman-doctor — women-doctors
In some nouns the plural form does not differ from the singular:
deer – deer
sheep – sheep
Sheep is black. Sheep are black.
Some nouns ending in -s (-ics) are usually singular and uncountable.
news, billiards, mathematics (or maths), physics, electronics, economics, politics, phonetics, athletics, gymnastics.
Most nouns ending in -f or -fe, drop the f and add ves.
half — halves
wolf — wolves