In grammar, a part of speech or also known as a word class, a lexical class, or a lexical category is a linguistic category of words or more precisely lexical items, which is generally defined by thesyntactic or morphological behaviour of the lexical item in question. Common linguistic categories include noun and verb, among others. There are open word classes, which constantly acquire new members, and closed word classes, which acquire new members infrequently if at all.
