dif·fu·sive \-üs]iv, -üz], ]ēv also ]əv\adjective 1.: having the quality of diffusing : tending to diffuse : characterized by diffusion 2.obsolete, of a people or group: acting as a mass of individuals having authority diffused throughout the entire membership • dif·fu·sive·ly\]ə̇vlē, -li\adverb • dif·fu·sive·ness\]ivnə̇s, ]ēv-\noun-es