The Spanish word 'negro' meaning 'black' comes directly from the Latin word 'niger', which meant 'shiny black'. This is a straightforward evolution where the Latin word maintained its core meaning of 'black' while simplifying in form as it developed into Spanish.

Some related Spanish words include 'negrura' (blackness), 'negrecer' (to blacken), and 'negrito' (diminutive form meaning 'little black one'). These words are all built from the same root 'negro' and expand the concept of blackness into different parts of speech and expressions.

In English, we can find several related words that share this Latin origin, such as 'negro' (now considered outdated and offensive), 'denigrate' (literally meaning 'to blacken', but used figuratively to mean 'to defame' or 'to belittle'), and 'nigella' (a genus of black-seeded flowering plants). The scientific term 'niger' is also used in some species names to indicate black coloring.