gratingn.[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.()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.()3. (Naut.) The strong wooden lattice used to cover a hatch, admitting light and air; also, a movable Lattice used for the flooring of boats.()a.[See Grate to rub harshy.] That grates; making a harsh sound; harsh.()n. A harsh sound caused by attrition.()