from The American Heritage® Dictionary of the English Language, 4th Edition
- n. An opening, such as a hole, gap, or slit.
- n. A usually adjustable opening in an optical instrument, such as a camera or telescope, that limits the amount of light passing through a lens or onto a mirror.
- n. The diameter of such an opening, often expressed as an f-number.
- n. The diameter of the objective of a telescope.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. An opening; an open space; a gap, cleft, or chasm; a passage perforated; a hole; as, an aperture in a wall.
- n. Something which restricts the diameter of the light path through one plane in an optical system.
- n. 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.
- n. The (typically) large-diameter antenna used for receiving and transmitting radio frequency energy containing the data used in communication satellites, especially in the geostationary belt. For a comsat, this is typically a large reflective dish antenna; sometimes called an array.
- n. The maximum angle between the two generatrices.
from the GNU version of the Collaborative International Dictionary of English
- n. The act of opening.
- n. An opening; an open space; a gap, cleft, or chasm; a passage perforated; a hole.
- n. The diameter of the exposed part of the object glass of a telescope or other optical instrument.
from The Century Dictionary and Cyclopedia
- n. The act of opening out or unfolding.
- n. An opening; a hole, orifice, gap, cleft, or chasm; a passage or perforation; any direct way for ingress or egress.
- n. In geometry, the space between two intersecting right lines.
- n. In optics, the diameter of the exposed part of the object-glass in a telescope or other optical instrument.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a device that controls amount of light admitted
- n. an man-made opening; usually small
- n. a natural opening in something
Middle English, from Latin apertūra, from apertus, past participle of aperīre, to open; see wer-4 in Indo-European roots.(American Heritage® Dictionary of the English Language, Fourth Edition)
Latin apertūra ("opening"), from apertus, past participle of aperīre ("to open, uncover"), opposed to operīre ("to close, cover"). See aperient. (Wiktionary)