The word 隔壁 is formed by combining two characters that each contribute a clear spatial concept: 隔 (gé) means "to separate" or "to partition", and 壁 (bì) means "wall". When placed together, they create a direct, literal image of being "separated by a wall". This visual-logical combination naturally extends to mean "next door" or "the adjoining room/space", as the most immediate neighbor is the one on the other side of a shared partition.