- noun a glass plate or metal mirror engraved with a large number of parallel lines or grooves, which produces a spectrum when light passes through it
- A surface with many fine parallel lines, grooves, or slits, which are extremely close together, and which serve to disperse light so as to produce a spectrum. Such a surface may be made of metal or glass, and may have over 15,000 lines, grooves, or slits, per centimeter. Also called grating (2).
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