An Etymological Dictionary of Astronomy and Astrophysics

1. An imperfection in an optical system whereby light from a point source is formed into an image as a straight line, ellipse, or circle. The rays of light in two perpendicular planes appear as two lines at right angles.
   
2. A common eye defect in which the unequal curvature of one or more refractive surfaces of the eye, usually the cornea, prevents light rays from focusing clearly at one point on the retina, resulting in blurred vision.

Etymology (EN): From astigmatic, from Gk. → a- “without” + stigmatos, from stigma “a mark, spot, puncture.”

Etymology (PE): 1) Nâgerâvari, from nâ- “without, un” + gerâ, stem of gerâyidan “to converge,” + -var, agent forming suffix, + -i, noun forming suffix.

2) The same as above with -bini “seeing, discerning”.