[ dahy-op-ter ]
/ daɪˈɒp tər /


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
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.

Nearby words

  1. diophantine equation,
  2. diophantus,
  3. diopside,
  4. diopsimeter,
  5. dioptase,
  6. dioptometer,
  7. dioptre,
  8. dioptric,
  9. dioptric aberration,
  10. dioptrics

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. 2019

Medicine definitions for dioptres


[ dī-ŏptər ]


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

The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.