A noun () is a word that generally functions as the name of a specific object or set of objects, such as living creatures, places, actions, qualities, states of existence, or ideas. Lexical categories (parts of speech) are defined in terms of the ways in which their members combine with other kinds of expressions. The syntactic rules for nouns differ between languages. In English, nouns are those words which can occur with articles and attributive adjectives and can function as the head of a noun phrase. "As far as we know, every language makes a grammatical distinction that looks like a noun verb distinction." History Word classes (parts of speech) were described by Sanskrit grammarians from at least the 5th century BC. In Yāska's Nirukta, the noun (nāma) is one of the four main categories of words defined. 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). The term used in Latin grammar was nōmen. All of these terms for "noun" were also words meaning "name". The English word noun is derived from the Latin term, through the Anglo-Norman noun. The word classes were defined partly by the grammatical forms that they take. In Sanskrit, Greek and Latin, for example, nouns are categorized by gender and inflected for case and number. Because adjectives share these three grammatical categories, adjectives are placed in the same class as nouns. Similarly, the Latin nōmen includes both nouns (substantives) and adjectives, as originally did the English word noun, the two types being distinguished as nouns substantive and nouns adjective (or substantive nouns and adjective nouns, or short substantives and adjectives). (The word nominal is now sometimes used to denote a class that includes both nouns and adjectives.) Many European languages use a cognate of the word substantive as the basic term for noun (for example, Spanish sustantivo, "noun"). Nouns in the dictionaries of such languages are demarked by the abbreviation s. or sb. instead of n., which may be used for proper nouns or neuter nouns instead. In English, some modern authors use the word substantive to refer to a class that includes both nouns (single words) and noun phrases (multiword units, also called noun equivalents). It can also be used as a counterpart to