Etymology
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astigmatism (n.)

"defect in the structure of the eye whereby the rays of light do not converge to a point upon the retina," 1849, coined by the Rev. William Whewell, English polymath, from Greek a- "without" (see a- (3)) + stigmatos genitive of stigma "a mark, spot, puncture," from PIE root *steig- "to stick; pointed" (see stick (v.)).

updated on November 30, 2017

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Definitions of astigmatism from WordNet

astigmatism (n.)
(ophthalmology) impaired eyesight resulting usually from irregular conformation of the cornea; common in nearsighted people;
Synonyms: astigmia
astigmatism (n.)
(optics) defect in an optical system in which light rays from a single point fail to converge in a single focal point;
Synonyms: astigmia
From wordnet.princeton.edu, not affiliated with etymonline.