The word 扩散 is formed by combining the character 扩, meaning "to expand" or "to enlarge", with the character 散, meaning "to scatter" or "to disperse". Together, they create a compound verb where 扩 emphasizes the broadening aspect and 散 emphasizes the spreading or dissemination aspect, resulting in the combined meaning of "to spread out" or "to diffuse", as in the diffusion of substances or ideas.