An Etymological Dictionary of Astronomy and Astrophysics

1. Outer; being on the outer side; situated or being outside, which is outside.
   

   2. Outside; an exterior part or surface.

Etymology (EN): From L. exterior “outward, outer, exterior,” comparative of exterus “on the outside, outward, outer, foreign,” itself a comparative of → ex- “out of.”

Etymology (PE): Boruni, from borun, variant of birun “out, the outside,” → out.