A noun is a part of speech typically denoting a person, place, thing, animal, or idea. In linguistics, a noun is a member of a large, open lexical category whose members can occur as the main word in the subject of a clause, the object of a verb, or the object of a preposition. Lexical categories are defined in terms of the ways in which their members combine with other kinds of expressions. The syntactic rules for nouns differ from language to language.