Aperture

Noun

 * 1) An opening; an open space; a gap, cleft, or chasm; a passage perforated; a hole; as, an aperture in a wall.
 * 2)  Something which restricts the diameter of the light path through one plane in an optical system.
 * 3)  The diameter of the aperture (in the sense above) which restricts the width of the light path through the whole system. For a telescope, this is the diameter of the objective lens. e.g. a telescope may have a 100 cm aperture.

Adjectives for Aperture
narrow; barred; grated; half-moon; yawning; ungarnished; ragged; circular; limiting.

Thesaurus
access; aisle; alley; ambulatory; arcade; artery; avenue; bore; breach; break; broaching; cavity; channel; chasm; check; chink; clearing; cleft; cloister; colonnade; communication; conduit; connection; corridor; covered way; crack; crevice; cut; defile; disclosure; discontinuity; exit; fenestra; ferry; fissure; fistula; fontanel; foramen; ford; gallery; gap; gape; gash; gat; gulf; hiatus; hole; hollow; inlet; interchange; intersection; interstice; interval; junction; lacuna; lane; laying open; leak; opening; opening up; orifice; outlet; overpass; pass; passage; passageway; perforation; pinhole; pore; portico; prick; puncture; railroad tunnel; rupture; slash; slit; slot; space; split; stoma; throwing open; traject; trajet; tunnel; uncorking; underpass; unstopping; vent; yawn