According to Wikipedia, "the English word mustang was likely borrowed from two essentially synonymous Spanish words, mestengo (or mesteño) and mostrenco. English lexicographer John Minsheu glossed both words together as 'strayer' in his dictionary of 1599. Both words referred to livestock defined as 'wild, having no master'."
Wikipedia goes on to explain that mostrenco may be of Portuguese origin, while mesteño has its origins in the Mesta – a powerful guild of sheep ranchers in mediaeval Spain, whose name is derived from the Latin word for 'mixed'. Both words date back to at least the 15th century.
© Haydn Thompson 2024