A Vacuum

1. A region of space that contains no matter.
2. (plural only "vacuums") A vacuum cleaner.
3. The condition of rarefaction, or reduction of pressure below that of the atmosphere, in a vessel, such as the condenser of a steam engine, which is nearly exhausted of air or steam, etc.
4. (physics) A spacetime having tensors of zero magnitude

The Latin in vacuo is sometimes used instead of in a vacuum (in free space).

(a region of space that contains no matter): vacancy, void

(vacuum cleaner): hoover (British)

(region of space that contains no matter): plenum