The character 相 originally depicts a person (目, an eye) looking at a tree (木), conveying the idea of "observing" or "appearing to one another", which extended to mean "mutually" or "each other". The character 互 is a pictograph of an ancient tool used for winding thread, whose interlocking form naturally suggests the idea of reciprocity and interconnectedness. When combined, 相 and 互 form a compound where both components reinforce and specify the same core concept of two-sided, reciprocal relationship or action, creating a single word whose meaning is more emphatic and complete than either part alone.