An Etymological Dictionary of Astronomy and Astrophysics

1. A space completely empty of matter but not achievable in practice on Earth.
   
2. A state of lowest energy in a → quantum field theory.

Etymology (EN): L. vacuum “an empty space, void,” noun use of neuter of vacuus “empty,” related to vacare “to be empty.”

Etymology (PE): Xala’ loan from Ar.