one 一 [yi] (the first tone) In Chinese characters, the number one is laid on its side, unlike the Roman numeralⅠwhich stands upright. As you would expect, it is written from left to right.
When this character is used as a primitive element, the keyword meaning is often discarded, since it is too abstract to be of much help. Instead, the single horizontal stroke takes on the meaning of floor or ceiling, depending on its position: if it stands above another primitive, it means ceiling; if below, floor.