1. Absence of matter; a space empty of matter or relatively empty of matter.
2. A space in which the pressure is significantly lower than atmospheric pressure.
3. A state of emptiness; a void.
4. A state of being sealed off from external or environmental influences; isolation.
5. Relating to, or used to create a vacuum.
6. Containing air or other gas at a reduced pressure.
7. Operating by means of suction or by maintaining a partial vacuum.
8. To use a vacuum cleaner on; clean with a vacuum cleaner: to vacuum rugs.
9. To treat with any vacuum device; such as, a vacuum drier.

A tool used to measure a vacuum with the ionization effect that an electron flow (from an incandescent filament to a charged grid) has on gas molecules.

1. The voltmeter whose sensitivity is increased by amplification.
2. A voltmeter that uses the rectifying and amplifying properties of electron devices and their associated circuits to secure desired characteristics; such as, high-input impedance, wide-frequency range, crest indications, peak-to-peak indications, and so on.

It is called a "vacuum-tube voltmeter" when its electron devices are vacuum tubes.

A system employing an exhaust fan that forces out foul or used air from a room in a building and provides fresh air from outside: Some firms, where dangerous or noxious processes take place, use vacuum ventilation in order to provide a healthy environment for the workers.

1. A device that determines the degree of vacuum in an electron tube by measuring the amount of ionization current in the tube.
2. A device; such as, a Geiger counter, that determines the amount of radiation in a medium by measuring the ionization generated by charged particles passing through a gaseous substance.

An electrometer is a device that uses, as an amplifier, a vacuum tube having a very high input impedance which is the measure of the opposition that an electrical circuit presents to the passage of an electric current when a voltage is applied.