The word "外面" is formed by combining two pictographic and ideographic characters. The first character, "外", originally depicted the moon outside a roof or boundary, conceptually representing "outside" or "external". It is joined with "面", a character that initially represented a face with an eye within an outline, extending to mean "surface" or "face". Together, they create a composite idea where "外" provides the concept of exteriority and "面" provides the concept of a frontal plane or area, merging to visually and notionally signify "the outward-facing surface" or "the exterior area", effectively picturing "the outside".