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
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)