An Etymological Dictionary of Astronomy and Astrophysics

Not closed.
Math.: → open interval; → open set.

Etymology (EN): O.E. open “not closed down, raised up,” also “uncovered, bare; plain, evident,” related to up; from P.Gmc. *upana (cf. O.N. opinn, Swed. öppen, Dan. aaben, O.Fris. epen, O.H.G. offan “open”), from PIE *upo “up from under, over;” cf. L. sub; Gk. hypo; O.Pers. upā (prep.) “under, with;” Av. upā, upa (prep.; prevb) “toward, with, on, in;”
Mod.Pers. bâ “with,” from abâ;
Skt. úpa (adv., prevb., prep.) “toward, with, under, on.”

Etymology (PE): Bâz “open,” from Mid.Pers. abâz-, apâc-, O.Pers. apa- [pref.] “away, from;” Av. apa- [pref.] “away, from,”
apaš [adv.] “toward the back;” cf. Skt. ápāñc “situated behind.”