The word 大便 is formed by combining two characters: 大 (dà), meaning "big" or "great", and 便 (biàn), meaning "convenient" or, in this context, "ordinary matter" or "waste". Together, they create a euphemistic compound that literally suggests "the big (or major) ordinary matter", which is a direct yet polite reference to human feces or the act of defecation, conceptually framing it as a significant bodily function.