In grammar, a noun is a word that represents a concrete or abstract thing, such as living creatures, places, actions, qualities, states of existence, and ideas.
[3] Word classes (parts of speech) were described by Sanskrit grammarians from at least the 5th century BC.
[4] The Ancient Greek equivalent was ónoma (ὄνομα), referred to by Plato in the Cratylus dialog, and later listed as one of the eight parts of speech in The Art of Grammar, attributed to Dionysius Thrax (2nd century BC).
In Sanskrit, Greek, and Latin, for example, nouns are categorized by gender and inflected for case and number.
Nouns have sometimes been characterized in terms of the grammatical categories by which they may be varied (for example gender, case, and number).
Nouns are frequently defined, particularly in informal contexts, in terms of their semantic properties (their meanings).
Nouns are described as words that refer to a person, place, thing, event, substance, quality, quantity, etc., but this manner of definition has been criticized as uninformative.
[8] Moreover, other parts of speech may have reference-like properties: the verbs to rain or to mother, or adjectives like red; and there is little difference between the adverb gleefully and the prepositional phrase with glee.
[9][10] Nouns can have a number of different properties and are often sub-categorized based on various of these criteria, depending on their occurrence in a language.
Nouns may be classified according to morphological properties such as which prefixes or suffixes they take, and also their relations in syntax – how they combine with other words and expressions of various types.
In some languages common and proper nouns have grammatical gender, typically masculine, feminine, and neuter.
The gender of a noun (as well as its number and case, where applicable) will often require agreement in words that modify or are used along with it.
In Modern English, even common nouns like hen and princess and proper nouns like Alicia do not have grammatical gender (their femininity has no relevance in syntax), though they denote persons or animals of a specific sex.
[14] Examples of acceptable and unacceptable use given by Gowers in Plain Words include:[14] Concrete nouns refer to physical entities that can, in principle at least, be observed by at least one of the senses (chair, apple, Janet, atom), as items supposed to exist in the physical world.
Similarly, some abstract nouns have developed etymologically by figurative extension from literal roots (drawback, fraction, holdout, uptake).
But inalienably possessed items are necessarily associated with their possessor and are referred to differently, for example with nouns that function as kin terms (meaning "father", etc.