Meaning of diopter

di•op•ter

Pronunciation: (dī-op'tur), [key]
— n.
  1. 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. Abbr.: 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.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.
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