Since the twelfth century, the phrase fijo d'algo ("son of something") and its contraction, fidalgo, were used in the Kingdom of Castile and in the Kingdom of Portugal to identify a type of nobility. In Portugal, the cognate remained fidalgo, which identified nobles of a similar status to a hidalgo in Spain. In the Kingdom of Aragón, the infanzón was the noble counterpart of the Castilian hidalgo. The pronunciation changes in Spanish occurred during the late Middle Ages, the letter-F sounding was lost, and replaced with the letter-H spelling and pronunciation of hidalgo. (see History of the Spanish language)
In the Spanish language of that period, in the phrase Hijo de algo, the word algo ("something") denotes "riches"; therefore, hidalgo was synonymous with "noble" and with ricohombre ("rich man"). In time, the term included the lower-ranking gentry, the untitled, lower stratum of the nobility who were exempted from taxation. The Siete Partidas (Leyes de Partidas), suggests that the word hidalgo derives from itálico ("italic"), a man with full Roman citizenship.
There is no evidence for another popular false etymology (folk etymology) that hidalgo is a corruption for hijo de godo ("son of the goth"). Every noble was called Godo (Goths) in the Kingdoms of Leon, Galicia, Portugal and Castile, as descendants of those from the Visigothic Kingdom of Toledo. The godo usage became common in the 11th century, when titles of nobility became common; and it remains a common and pejorative usage in rural regions of Iberia.
In the previous Visigoth monarchies, the condition of the hidalgo was that of a freeman without land wealth, but with the nobleman's rights to wear arms and to be exempt from taxation, in compensation for military service; the military obligation and the social condition remained in force by the Fuero Juzgo law. The Goths used the terms hidalgo and Vesi to mean the "good men". In Old Castile, the byname hidalgo ("son of the good one") was used alternatively with the toponymical term Vesi ("sons of the mountain").