There are three main ways in which we can put nouns together so that one modifies the other:
1. noun + noun:
a bicycle factory
a war film
the table leg.
2. noun + ’s + noun:
my sister’s car
a bird’s nest
cow’s milk.
3. noun + preposition + noun:
the top of the page
a man from London
a book on modern music
a feeling of disappointment.
Unfortunately, the exact differences between the three structures are complicated and difficult to analyse – this is one of the most difficult areas of English grammar. We use the noun + ’s + noun structure to talk about parts of people’s and animals’ bodies, (e.g. an elephant’s trunk) but to talk about parts of non-living things we usually use noun + noun structure (e.g. the table leg; NOT the table’s leg.)
With words like top, bottom, front, back, side, inside, outside, beginning, middle, end, part we usually prefer the noun + preposition + noun structure:
the top of the page (not: the page top)
the back of the bus (not: the bus back)
the bottom of the glass (not: the glass bottom)
the end of the film (not: the film end)
There are, however, some common exceptions:
the water’s edge
the seaside
the roadside
a mountain top.
We also prefer the noun + preposition + noun structure with words that refer to units, selections and collections, like piece, slice, lump, bunch, blade, pack, herd, flock, group, and so on (e.g. a piece of paper; a bunch of flowers).
