[dif.fus.er] n (ca. 1679) 1: one that diffuses: as a: a device (as a reflector) for distributing the light of a lamp evenly b: a screen (as of cloth or frosted glass) for softening lighting (as in photography) c: a device (as slats at different angles) for deflecting air from an outlet in various directions
2: a device for reducing the velocity and increasing the static pressure of a fluid passing through a system