A grammatical class of words with a potentially unlimited membership and which have content meaning such as adjectives, nouns, and verbs that children begin to use between 9 months and 1.5 years of age. It is a word to which meaning can be assigned. An adjective is a word that belongs to a class whose members modify nouns. It specifies the properties or attributes of a noun referent, where a referent is a word used to represent things and experiences in the real or imagined world. As a member of a syntactic class, a noun is a word acting on subjects and objects of verb, and indirect object of the verb. It refers to people, places, things, ideas or concepts. A verb is a member of a syntactic class of words such as those that signal actions and events, constitute a minimal predicate in a clause, and govern the number and type of constituents that may occur.
See Closed-class words, Count (or countable) words, Double object nouns, Grammaticization (or grammaticalization), Language development, Proper noun, Syntax