RULES FOR THE FORMATION OF COMPOUNDS
I Two nouns used together as a name form a compound noun unless:
(a) The first is used in a descriptive or attributive sense, that is, is really an adjective, or
(b) The two are in apposition.
Various uses of the noun as an adjective, that is, in some qualifying or attributive sense are when the noun conveys the sense of:
1. “Made of;” leather belt, steel furniture.
2. “Having the shape, character, or quality of;” diamond pane, iron ration, bull calf.
3. “Pertaining to, suitable for, representing;” office desk, labor union.
4. “Characterized by;” motor drive.
5. “Situated in, and the like;” ocean current, city life.