Nouns -> Adjectives

Noun as Adjective

As you know, a noun is a person, place or thing, and an adjective is a word that describes a noun:

adjective	noun
clever	teacher
small	office
black	horse

Sometimes we use a noun to describe another noun. In that case, the first noun "acts as" an adjective.

noun as adjective	noun
science	teacher
ticket	office
race	horse

The "noun as adjective" always comes first

If you remember this, it will help you to understand what is being talked about:

• a race horse is a horse that runs in races
• a horse race is a race for horses
• a boat race is a race for boats
• a love story is a story about love
• a war story is a story about war
• a tennis ball is a ball for playing tennis
• tennis shoes are shoes for playing tennis
• a computer exhibition is an exhibition of computers
• a bicycle shop is a shop that sells bicycles

The "noun as adjective" is singular

Just like a real adjective, the "noun as adjective" is invariable. It is usually in the singular form.

Right		Wrong
boat race	boat races	NOT boats race, boats races
toothbrush	toothbrushes	NOT teethbrush, teethbrushes
shoe-lace	shoe-laces	NOT shoes-lace, shoes-laces

In other words, if there is a plural it is on the real noun only.

A few nouns look plural but we usually treat them as singular (for example news, billiards, athletics). When we use these nouns "as adjectives" they are unchanged:

• a news reporter, three news reporters
• an athletics trainer, fifty athletics trainers

Exceptions: When we use certain nouns "as adjectives" (clothes, sports, customs, accounts, arms), we use them in the plural form:

• clothes shop, clothes shops
• sports club, sports clubs

(https://www.englishclub.com/grammar/nouns-adjective.htm)