Lexical category refers to a set of words that share similar grammatical properties. There are several other terms used interchangeably with lexical category such as part of speech, word class, syntactic category, and grammatical category. These terms are used to describe the function of words in a sentence such as noun, verb, adjective, adverb, preposition, conjunction, and interjection. Each of these categories has its own set of rules for usage and placement within a sentence. The study of lexical categories is essential to understanding and effectively using language. Synonyms for lexical category help to explain the function of words and their relationship to one another within sentences.