Proper noun

A proper noun is a noun that in its primary application refers to a unique entity, such as London, Jupiter, Sarah, or Microsoft, as distinguished from a common noun, which usually refers to a class of entities (city, planet, person, corporation), or non-unique instances of a specific class (a city, another planet, these persons, our corporation). Some proper nouns occur in plural form (optionally or exclusively), and then they refer to groups of entities considered as unique (the Hendersons, the Everglades, the Azores, the Pleiades). Proper nouns can also occur in secondary applications, for example modifying nouns (the Mozart experience; his Azores adventure), or in the role of common nouns (he's no Pavarotti; a few would-be Napoleons). The detailed definition of the term is problematic and to an extent governed by convention.

A distinction is normally made in current linguistics between proper nouns and proper names. By this strict distinction, because the term noun is used for a class of single words (tree, beauty), only single-word proper names are proper nouns: Peter and Africa are both proper names and proper nouns; but Peter the Great and South Africa, while they are proper names, are not proper nouns. The term common name is not much used to contrast with proper name, but some linguists have used the term for that purpose. Sometimes proper names are called simply names; but that term is often used more broadly. Words derived from proper names are sometimes called proper adjectives (or proper adverbs, and so on), but not in mainstream linguistic theory. Not every noun or noun phrase that refers to a unique entity is a proper name. Blackness and chastity are common nouns, even if blackness and chastity are considered unique abstract entities.