the combination of a prism with grooves cut into one surface that allows light to be dispersed into a spectrum. The use of the grooves (called a grating) causes the spectrum to emerge from the prism at an exact angle. Without the grating the light must be passed through a small slit for the spectrum to be measured. The GALEX grism will allow the spectra of many hundreds of stars and galaxies to be measured from a single image of the sky.
a combination of a prism, which splits light into individual spectra, and a grating through which light is transmitted
a transmission grating mounted (or etched into a prism-shaped dielectric substrate