Aperture /(?; 135)/

Ap·er·ture

Aperture

n.
  1. The act of opening. [Obs.]
  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. The diameter of the exposed part of the object glass of a telescope or other optical instrument; as, a telescope of four-inch aperture. (Opt.)