The Spanish word 'brujo' (meaning 'male witch' or 'sorcerer') comes from the Medieval Spanish word 'bruxa' (meaning 'witch'), which in turn derives from the Proto-Celtic word 'brixta', meaning 'spell' or 'magic'. The word underwent a gender change from the feminine 'bruxa' to create the masculine form 'brujo', following the typical Spanish pattern of changing -a to -o to indicate masculine gender.

A closely related Spanish word is 'bruja', which is the modern feminine form meaning 'witch'. This word maintains a closer connection to the Medieval Spanish 'bruxa' in both form and meaning. The pair bruja/brujo demonstrates the common Spanish pattern of gender marking through the final vowel (-a for feminine, -o for masculine).

While there aren't direct cognates in modern English, the Celtic origin of this word reminds us that beliefs in magic and witchcraft were widespread across European cultures. The closest English connections would be through borrowed terms like 'bruxism' (teeth-grinding, named after medieval beliefs about witches grinding their teeth), though this is a modern medical term rather than a direct etymological relative.