grating

n. [ See 2d Grate. ] 1. A partition, covering, or frame of parallel or cross bars; a latticework resembling a window grate; as, the grating of a prison or convent. [ 1913 Webster ]

2. (Optics) A system of close equidistant parallel lines or bars, esp. lines ruled on a polished surface, used for producing spectra by diffraction; -- called also diffraction grating. Gratings have been made with over 40, 000 such lines to the inch, but those with a somewhat smaller number give the best definition. They are used, e. g., to produce monochromatic light for use in optical instruments such as spectrophotometers. [ Webster 1913 Suppl. ]

3. pl. (Naut.) The strong wooden lattice used to cover a hatch, admitting light and air; also, a movable Lattice used for the flooring of boats. [ 1913 Webster ]