The Spanish word 'charro' comes from the Basque word 'txar', meaning 'defective' or 'weak'. While this etymology might seem surprising given the modern meaning, the term evolved significantly in Spanish. Originally likely used as a somewhat derogatory term for rural people, it came to specifically refer to horsemen or cowboys from Salamanca, Spain. The meaning later expanded in Mexico, where 'charro' became a prestigious term for a traditional Mexican horseman, skilled in horsemanship and rodeo-like activities, wearing distinctive elaborate clothing and participating in charreada (Mexican rodeo).

This semantic evolution from a negative Basque term to a respected cultural symbol is a fascinating example of how words can completely transform their connotations over time. The Mexican charro has become such an important cultural figure that charrería (traditional Mexican horsemanship) was declared an Intangible Cultural Heritage by UNESCO.

While 'charro' is quite unique in Spanish and doesn't have many common related words, you might encounter 'charrería' (the art and practice of traditional Mexican horsemanship) and 'charreada' (a Mexican rodeo), both derived directly from 'charro'.

There aren't any common English words directly related to 'charro' since it comes from Basque rather than the Indo-European language family that English belongs to. However, English has borrowed the word 'charro' itself when referring to Mexican cowboys and their traditional dress.