In linguistics, a noun or noun substantive is a lexical category which is efined in terms of how its members combine with other kinds of expressions. Since different languages have different inventories of kinds of expressions, the definition of noun will differ from language to language. In English, nouns may be defined as those words which can co-occur with definite articles and attributive adjectives, and function as the head of a noun phrase. The noun can be replaced by a pronoun of first person, second person, or even third person. Also the noun is known for being one of the eight parts of speech.