aperturen.[L. apertura, fr. aperire. See Aperient.]1. The act of opening.()2. An opening; an open space; a gap, cleft, or chasm; a passage perforated; a hole; as, an aperture in a wall.()An aperture between the mountains. (Gilpin.)The back aperture of the nostrils. (Owen.)3. (Opt.) The diameter of the exposed part of the object glass of a telescope or other optical instrument; as, a telescope of four-inch aperture.()()