Noun Adjuncts (noun + noun)
In English we can put two nouns together. The first noun is used as an adjective to modify the second noun and is called a noun adjunct. The first noun is almost always singular because it follows the rule for adjectives, which do not have plural forms in English.
N1 N2 can mean that
a. N1 is a kind of N2 (a grammar book is a kind of book)
b. N1 is an object of an implied verb (an apple tree is a tree that produces apples)
It is important to understand that N2 is the thing and N1 is the kind or type:
a rose bush is a bush
a wrist watch is a watch
computer paper is paper
N1 is singular, even if the phrase
My mother planted a rose bush in the garden.
I bought a new table lamp.
Bobby takes the school bus to school.
The school ordered fifty new grammar books.
That man makes bird cages.
Mrs. Taylor bought some new baby clothes.
We can use a number with N1 to
make a compound adjective. Since the number and noun make one unit, we
use a hyphen to join them. Note that N1
remains singular because it is being used as an
a three-car garage
a ten-speed bicycle
a twenty-dollar bill
If we use a number to refer to the second noun (how many), we do not
use a hyphen:
two grammar books
five rose bushes
We can use a number to refer to the second noun (how many) and a
number with the first noun (compound adjective). In that case, there
is no hyphen after the first number, but the second number is still
used with a hyphen because it forms a compound adjective.
two ten-dollar bills
four three-bedroom homes