The word 日期 is formed by combining two meaningful characters: 日 (rì), which originally meant "sun" but by extension signifies "day", and 期 (qī), which carries the meaning of a "set time", "period", or "appointed date". Conceptually, the compound is built by taking the fundamental unit of 日 ("day") and specifying it with 期 ("designated period") to create the integrated idea of a specific point or span on the calendar, thus forming the complete concept for "date".