Castilian is a term that is related to the people or things that are associated with the Castile region in Spain. However, there are several synonyms for Castilian that are widely used. One of the synonyms for Castilian is the Spanish language, which is also known as Castilian in the country. Another synonym for the term is the Castillian language, which is the early form of the Spanish language that was spoken in the Castile region of Spain. In addition to these, Castilian is also synonymous with the Castilean dialect and the Castilian people, who are the residents of the Castile region and usually have the traditional cultural and linguistic traits of the region.