compoundnoun

A compound noun is a noun formed by combining two or more words to function as a single nominal unit. In English, compounds can designate concrete objects, abstract concepts, or roles, and their meaning may be fully predictable from the parts or idiomatic and specialized.

Orthography and forms vary. Closed forms join the elements into one word (bookcase, toothpaste); open forms separate them with a space (coffee table, high school); hyphenated forms connect them with a hyphen (mother-in-law, well-being). The choice often depends on tradition, frequency, and clarity, and different style guides may differ on preferred spellings.

Most English compound nouns are noun-noun and typically right-headed: the rightmost noun supplies the main category while the left provides a modifier (sunlight, bookshelf). There are also adjective-noun compounds (greenhouse), and less commonly other patterns such as noun-verb blends used as nouns. The semantics of compounds range from transparent to opaque; some convey precise, literal senses, while others acquire new meanings not easily predicted from the components.

Usage and history: Compound nouns are highly productive in English, especially for technology, culture, and everyday objects. They can evolve from phrases into single words, or remain open or hyphenated as usage shifts. Cross-linguistic differences in compounding reflect diverse syntactic and orthographic conventions.

See also: compounding, noun, morphology.