The Spanish word 'negrero' (meaning 'slave trader') comes from combining the Spanish word 'negro' (meaning 'black') with the occupational suffix '-ero'. The word 'negro' itself derives from the Latin word 'niger', which meant 'black' or 'shiny black'. The suffix '-ero' is commonly added to nouns in Spanish to indicate a person who works with or deals in something (like 'panadero' for baker). In this case, the combination tragically refers to someone who traded in enslaved Black people.

The most obvious related Spanish word is 'negro' meaning 'black', which is much more commonly used and is one of the basic color words that Spanish students learn early on. This word maintains the original meaning from Latin 'niger' of describing the color black.

The English word 'Negro' (now considered dated and offensive) comes from the same Latin root 'niger'. Additionally, the scientific terms 'niger' and 'nigrescent' (becoming black or darkish) are direct borrowings from this Latin root. The word 'denigrate' (to criticize unfairly; blacken someone's reputation) also contains this Latin root, combined with the prefix 'de-'.