A noun can modify another noun that follows it. As a modifier, the first noun gives specific information about the following noun. In nearly all cases, the noun that acts as the modifier is in singular form.
They do not have vegetable soup, but they do have chicken soup and tomato soup.
In the sentence, the nouns vegetable, chicken and tomato are modifiers. They modify soup. Without the modifiers, we would not know what soup they have or do not have, and all we would know if they have soup.
As stated, the modifying noun is placed attributively; that is, before the noun it describes to add meaning to it (the noun being modified). For example, we know what a ship is, but do we know what type of ship it is or what it is used for? By using a noun acting as an adjective before the noun ship, we get to know what ship it is – a battleship, cargo ship, container ship, cruise ship, merchant ship, sailing ship, spaceship, or supply ship, or even an enemy ship or a pirate ship.
Business/girls’/language/village school – She is a teacher in a language school.
Corner/gift/pet/shoe shop – The gift shop offers a small selection of leather goods.
Family/farm/pet/police/sheep/sniffer/toy dog – The police dog was sniffing round the detainee’s heels.
Council/country/dream/farm/mansion/tree/summer house – They rented a council house when they got married.
We are renovating the old farm buildings.
They spent the weekends doing the flower bed.
She kept her money box under her bed.
The road accident injured five people.
He still keeps the library books after they have expired.
When a noun used as a modifier is combined with a number expression, the noun is singular and a hyphen is used.
He took a half-year course in raising pigeons.
He does a one-man show in an open-air theatre.
The pilot overshot the runway and crashed his two-seater aircraft.
She plays in a five-girl rock band.
Noun modifiers of noun modifiers are used together.
He sprawled on the family room couch reading newspaper.
That one over there is a toy factory building.
You can get your rock garden tools in this store.
His company car workshop is demanding overdue payments.
Their two-partner computer business is expanding fast.
The family lived in a four-bedroom country house.
He will have to serve a six-year prison sentence for attempted murder.
The 50-acre apple orchard attracts hordes of tourists.
In the first example above, the family is a noun modifier and room to is a noun modifier. This means the noun modifier family is modifying the noun modifier room. In the lower list, each example has two noun modifiers modifying one noun; for example, two-partner and computer together modify the noun business.