The word 室友 is formed by directly combining two conceptual ideas represented by individual characters: 室 (shì), meaning "room", and 友 (yǒu), meaning "friend" or "companion". The formation is purely ideographic, creating a new, compound concept that visually and logically denotes a "room friend", that is, a person who shares a living space with you. It’s a straightforward semantic fusion where the first character defines the shared location (room) and the second defines the relational nature of the person within it (friend), instantly evoking the idea of a roommate.