Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. A unit of measurement of the refractive power of lenses equal to the reciprocal of the focal length measured in meters.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. A unit of measure of the power of a lens or mirror, equal to the reciprocal of its focal length in meters. Myopia is diagnosed and measured in diopters.
  • n. Any lens system, such as a telescope.
  • n. A theodolite or similar surveyor’s angle measuring device.
  • n. An alidade.
  • n. A surgical speculum.
  • n. An instrument for drawing the skull by projections.

from the GNU version of the Collaborative International Dictionary of English

  • n. An optical instrument, invented by Hipparchus, for taking altitudes, leveling, etc.

from The Century Dictionary and Cyclopedia

  • n. An ancient form of theodolite.
  • n. The alidade or index arm of a graduated circle.
  • n. An instrument used in craniometry for obtaining projections of the skull.
  • n. A dioptric.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. a unit of measurement of the refractive power of a lens which is equal to the reciprocal of the focal length measured in meters; used by oculists

Etymologies

Obsolete diopter, an instrument for measuring angles, from Latin dioptra, from Greek dioptrā : dia-, dia- + optos, visible; see okw- in Indo-European roots.
(American Heritage® Dictionary of the English Language, Fourth Edition)
From French dioptre, from Latin dioptra, from Greek διοπτρα ("to see through"). (Wiktionary)

Examples

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  • (n): in optics and cinematography, part of the lens or viewfinding system that can be adjusted to compensate for one's own particular eyesight, allowing one to see the groundglass clearly.

    January 18, 2009