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diopter

[dahy-op-ter]
noun
  1. Optics. a unit of measure of the refractive power of a lens, having the dimension of the reciprocal of length and a unit equal to the reciprocal of one meter. Abbreviation: D
  2. an instrument, invented by Hipparchus, to measure the apparent diameter of the sun or moon or to estimate the size or elevation of distant objects.
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Also especially British, di·op·tre.

Origin of diopter

1585–95; < Latin dioptra < Greek: instrument for measuring height or levels, equivalent to di- di-3 + op- (for ópsesthai to see) + -tra noun suffix of means
Related formsdi·op·tral, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for dioptre

dioptre

US diopter

noun
  1. a unit for measuring the refractive power of a lens: the reciprocal of the focal length of the lens expressed in metres
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Derived Formsdioptral, adjective

Word Origin

C16: from Latin dioptra optical instrument, from Greek, from dia- through + opsesthai to see
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

dioptre in Medicine

diopter

(dī-ŏptər)
n.
  1. A unit of measurement of the refractive power of lenses equal to the reciprocal of the focal length measured in meters.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.