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

A specialized prism for taking spectra.

A ruled prism which disperses the light into a spectrum. The GALEX grism is slitless so it acts on the entire field of view. (See the Mission & Instrument Overview in GR1 documentation.)

A grism is a combination of a prism and grating arranged to keep light at a chosen central wavelength undeviated as it passes through.