The word 禽兽 is formed by combining two characters, each representing a broad class of animals. 禽 (qín) historically refers to birds or fowls, creatures of the air, while 兽 (shòu) refers to beasts or quadrupedal mammals, creatures of the land. Their union creates a compound that conceptually encompasses the entire animal kingdom by uniting these two fundamental, ancient categories of living creatures. Thus, the term is constructed not by grammar, but by a holistic, categorical merging to represent the idea of "all animals" or, by metaphorical extension, a brutish nature devoid of human civility.