Vacuum \Vac"u*um\, n.; pl. E. Vacuums, L. Vacua. [L., fr. vacuus empty. See Vacuous.]

1. (Physics) A space entirely devoid of matter (called also, by way of distinction, absolute vacuum); hence, in a more general sense, a space, as the interior of a closed vessel, which has been exhausted to a high or the highest degree by an air pump or other artificial means; as, water boils at a reduced temperature in a vacuum.

Source: Webster's Revised Unabridged Dictionary (1913)