The Spanish word 'melena' actually has two distinct etymological origins, leading to two different meanings in modern Spanish. The first meaning, referring to 'long hair' or an 'ox-yoke cushion', comes from Arabic. It can be traced back to the Classical Arabic word 'mulayyinah' meaning 'cushioning', which evolved into Andalusi Arabic 'muláyyina' before entering Spanish.

The second meaning of 'melena' in Spanish, used in medical contexts to refer to black stool, comes from the Ancient Greek word 'mélaina' (μέλαινα), which meant 'black' (specifically the feminine form of the adjective). This technical medical term maintains a direct connection to its Greek origin in both form and meaning.

The Spanish word 'melena' is quite unique in its etymology and doesn't have many commonly used, simpler Spanish relatives. However, in medical Spanish, you might encounter related terms like 'melanina' (melanin) or 'melanoma', which share the Greek root meaning 'black' with the medical sense of 'melena'.

While the Arabic-derived meaning of 'melena' (long hair/cushion) doesn't have clear English cognates, the Greek-derived medical term has several English relatives. English words like 'melanin' (the dark pigment in skin and hair), 'melancholy' (originally believed to be caused by 'black bile'), and 'melanoma' (a type of skin cancer) all share the same Greek root 'melas/melaina' meaning 'black'. Understanding this connection can help remember the medical meaning of 'melena' as referring specifically to black stool.