An Etymological Dictionary of Astronomy and Astrophysics

General: A group or series of eight.
Chemistry: A stable group of eight electrons which constitutes the outer electron shell of an atom of an inert gas (except helium whose only electron shell contains two electrons).

Etymology (EN): From → oct-, octa- + -et, as in duet.

Etymology (PE): Haštâyé, from haštâ “eightfold” + (y)é nuance suffix, as in dotâyé, → doublet.