Grammar

2.174 Modifying using nouns: noun modifiers

Nouns can be used as modifiers in front of other nouns when you want to give more specific information about someone or something. Sometimes, when nouns are used like this they become fixed expressions which are called compound nouns, (see paragraphs 1.84 to 1.93).

When the nouns used in front of other nouns are not in fixed expressions, they are called noun modifiers.

...the car door.
...tennis lessons.
...a football player.
...cat food.
...the music industry.
...a surprise announcement.