The word "宇宙" (yǔzhòu, meaning "cosmos" or "universe") is formed through the conceptual combination of two ancient characters, each representing a fundamental dimension of existence. "宇" originally depicted the eaves of a house, extending to mean "all space" (everywhere under the heavens), while "宙" referred to the ridgepole or axis of a building, extending to mean "all time" or eternity (the endless duration from past to future). By joining them, the compound creates a single, profound concept that encapsulates the totality of all spatial expanse and all temporal duration, the entire physical reality.