In linguistics, a noun or noun substantive is a lexical category which is defined in terms of how its members combine with other grammatical kinds of expressions. Since different languages have different inventories of grammatical categories, the definition of noun will differ from language to language. In English, nouns can be defined as those morphological stems that form words which can co-occur with (in)definite articles and attributive adjectives, and function as the head of a noun phrase.