Note: in England football team coach can you see a "hidden" "noun as adjective"? Look at the word "football" (foot-ball). These two nouns (foot+ball) have developed into a single noun (football). This is one way that words evolve. Many word combinations that use a "noun as adjective" are regarded as nouns in their own right, with their own dictionary definition. But not all dictionaries agree with each other. For example, some dictionaries list "tennis ball" as a noun and other dictionaries do not.