stylistic:style_transfer
Etymology

The term castellano is related to Castile (Castilla or archaically Castiella), the kingdom where the language was originally spoken. The name Castile, in turn, is usually assumed to be derived from castillo ('castle').

In the Middle Ages, the language spoken in Castile was generically referred to as Romance and later also as Lengua vulgar. Later in the period, it gained geographical specification as Romance castellano (romanz castellano, romanz de Castiella), lenguaje de Castiella, and ultimately simply as castellano (noun).

Different etymologies have been suggested for the term español (Spanish). According to the Royal Spanish Academy, español derives from the Occitan word espaignol and that, in turn, derives from the Vulgar Latin * hispaniolus ('of Hispania'). Hispania was the Roman name for the entire Iberian Peninsula.

There are other hypotheses apart from the one suggested by the Royal Spanish Academy. Spanish philologist Ramón Menéndez Pidal suggested that the classic hispanus or hispanicus took the suffix -one from Vulgar Latin, as happened with other words such as bretón (Breton) or sajón (Saxon).