The term 'Horses' Relatives' can be summarized by the crossword solution ASSES, which is a 5-letter word. ASSES are members of the Equidae family, which also includes horses, zebras, and donkeys. They are herbivorous mammals that are found in many parts of the world, including Africa, Asia, and Europe. ASSES are known for their hardiness and strength, and they have been used as beasts of burden for centuries.