The word 另外 is formed by combining the character 另, which carries the core meaning of "separate" or "another", with 外, meaning "outside" or "external". This combination semantically fuses the idea of a distinct, separate entity with the notion of being outside the current frame of reference. The resulting compound conceptually paints a picture of "an additional, separate item existing outside the set already under consideration", thereby naturally conveying the sense of "in addition" or "another".