You searched for: “aperture
aperture
The clear diameter of the light-gathering surface of a telescope.

For a refractor telescope, it is the diameter of the objective lens, and for a reflecting telescope, it is the diameter of the primary mirror.

This entry is located in the following unit: Astronomy and related astronomical terms (page 2)
A hole or an opening. (2)
Word Entries at Word Info: “aperture
aperture (s) (noun), apertures (pl)
1. An opening; such as, a hole, a gap, or a slit: There was an aperture in the window after Sam threw a rock at the building.
2. A fixed or an adjustable opening in an optical instrument; such as, a camera or a telescope, which limits the amount of light passing through a lens or onto a mirror: While he was taking pictures, Pete adjusted the aperture on his camera several times.
A hole or opening.
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A gap or hole.
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This entry is located in the following unit: apert-, aperi- + (page 1)
A unit at Word Info related to: “aperture
(Latin: to stand open, to split; opening, aperture, gap; to yawn)
(Greek: door, gate, entrance; orifice, an aperture or hole opening into a bodily cavity; indicating the portal vein)
(Greek > Latin: that which binds tightly, press together; band, lace; hence, muscle that closes an aperture of the body; a ringlike band of muscle fibers that constricts a passage or closes a natural orifice)