dioptral

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.
Also, especially British, dioptre.


Origin:
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

dioptral, adjective
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World English Dictionary
dioptre or diopter (daɪˈɒptə)
 
n
a unit for measuring the refractive power of a lens: the reciprocal of the focal length of the lens expressed in metres
 
[C16: from Latin dioptra optical instrument, from Greek, from dia- through + opsesthai to see]
 
diopter or diopter
 
n
 
[C16: from Latin dioptra optical instrument, from Greek, from dia- through + opsesthai to see]
 
di'optral or diopter
 
adj

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Medical Dictionary

diopter di·op·ter (dī-ŏp'tər)
n.
Abbr. D.
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
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