aperture

American  

[ap-er-cher] / ˈæp ər tʃər /

noun

1. an opening, as a hole, slit, crack, gap, etc.

2. Also called aperture stop.  Optics. an opening, usually circular, that limits the quantity of light that can enter an optical instrument.

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aperture British  

/ ˈæpətʃə /

noun

1. a hole, gap, crack, slit, or other opening

2. physics

   1. a usually circular and often variable opening in an optical instrument or device that controls the quantity of radiation entering or leaving it

   2. the diameter of such an opening See also relative aperture

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Other Word Forms

• apertural adjective
• apertured adjective

Etymology

Origin of aperture

1400–50; late Middle English < Latin apertūra an opening, equivalent to apert ( us ) opened (past participle of aperīre; aper ( i )- ( aperient ) + -tus past participle suffix) + -ūra -ure

Example Sentences

"Synthetic aperture imaging -- the method that allowed the Event Horizon Telescope to image a black hole -- works by coherently combining measurements from multiple separated sensors to simulate a much larger imaging aperture."

From Science Daily • Jan. 10, 2026

The latest version, made by ASML, performs high numerical aperture extreme ultraviolet lithography.

From The Wall Street Journal • Nov. 3, 2025

A hermit crab will inspect a shell with care, running antennae and claws over its contours, before delicately lowering its rear end into the aperture.

From Slate • Aug. 19, 2025

"I learned how to shoot at night, adjust shutter speed and aperture," said Keerthi, who lives in the Tenkasi district.

From BBC • Mar. 14, 2025

It was as though he’d been peering through a narrow lens and the aperture began to widen to take in the entire landscape in a kind of efflorescent illumination.

From "Endgame" by Frank Brady