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Classifying expressions: noun + noun or preposition structure?

Classifying expressions: a sheepdog​

The noun + noun structure is mostly used to make ‘classifying’ expressions, which name a particular kind of thing.

  • mountain plants (a special group of plants)
  • mineral water (a sort of water)
  • a sheepdog (a particular kind of dog)

We use noun + noun especially to talk about things that belong to common well-known classes (so that the two nouns really describe a single idea). In other cases we prefer a preposition structure. Compare:

  • the postman, the milkman (well-known kinds of people who may call regularly at a British home)
  • a man from the health department (not a regular kind of visitor)

More examples:

  • He was reading a history book. (a common class of book)
    He was reading a book about the moon. (not a moon book)
  • She was sitting at a corner table in the restaurant. (Restaurants often have corner tables.)
    Who’s the girl in the corner? (not Who’s the corner girl?)
  • What does that road sign say?
    She was showing signs of tiredness. (not … tiredness signs.)

Containers: a matchbox; a box of matches​

Noun + noun is used for particular kinds of container.

  • a matchbox
  • a paint tin
  • a coffee cup

But we use the preposition structure (with of) to talk about a container together with its contents.

  • a box of matches
  • a tin of paint
  • a cup of coffee

Units, selections and collections: piece, group, etc​

We also prefer the of-structure with words that refer to units, selections and collections, like piece, slice, lump (of sugar), bunch (of flowers), blade (of grass), pack (of cards), herd, flock, group and so on.

  • a piece of paper (not a paper piece)
  • a bunch of flowers (not a flower bunch)

‘made of’: a silk dress; silken skin​

Noun + noun is normally used to say what things are made of.

  • a silk dress
  • a stone bridge
  • an iron rod
  • a gold ring

In older English, the of-structure was more common in this case (e.g. a dress of silk, a bridge of stone), and it is still used in some metaphorical expressions.

  • He rules his family with a rod of iron.
  • The flowers were like a carpet of gold.

A few pairs of nouns and adjectives (e.g. gold, golden) are used as modifiers with different meanings. Generally the noun simply names the material something is made of, while the adjective has a more metaphorical meaning. Compare:

  • a gold watch
  • silk stockings
  • a lead pipe
  • a stone roof
  • golden memories
  • silken skin
  • a leaden sky (grey and depressing)
  • a stony silence

But wooden and woollen just mean ‘made of wood/wool’.