An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A diverging lens having one surface convex and the opposite surface concave.

→ convex; → concave; → lens.

Prefix meaning "outside; outer; external" used in the formation of compound words: exoplanet, exosphere, exocentric.

From Gk. exo "outside," used in forming scientific terms, → ex-.

Borun-, from borun "out, the outside" (Mid.Pers. bêron, from bê "outside, out, away" + rôn "side, direction;" Av. ravan- "(course of a) river").