An Etymological Dictionary of Astronomy and Astrophysics

Freedom from spherical aberration and coma.

Etymology (EN): Aplanatism, from aplanatic, from a- “negation prefix” + Gk. plane “wandering,” from
planasthai “to wander” + -tic adjective-forming suffix.

Etymology (PE): Nâbirahi, from nâ- “negation prefix” + birah “a devious path; a wanderer, who deviates, errs,” + -i noun affix.