The word 窗户 is formed through a conceptual combination where two characters, each carrying a related core idea, merge to create a single, more complete meaning. The first character, 窗, specifically means "window" as an opening for light and air. The second, 户, originally meant a single-leaf door or a household entrance. Together, they combine the ideas of a light-opening (窗) and a functional opening in a wall (户), resulting in a reinforced and more general term for "window", effectively blending the concepts of aperture and transparency into one unified object.