vacuum tube

American  

noun

1. especially British, vacuum valve.  an electron tube from which almost all air or gas has been evacuated: formerly used extensively in radio and electronics.

2. a sealed glass tube with electrodes and a partial vacuum or a highly rarefied gas, used to observe the effects of a discharge of electricity passed through it.

---

vacuum tube British  

noun

1. another name for valve

---

vacuum tube Scientific  

1. An electron tube from which all air has been removed. The vacuum ensures transparency inside the tube for electric fields and moving electrons. Most electron tubes are vacuum tubes; cathode-ray tubes, which include television picture tubes and other video display tubes, are the most widely used vacuum tubes. In other electronic applications, vacuum tubes have largely been replaced by transistors.

---

Etymology

Origin of vacuum tube

First recorded in 1775–85

Example Sentences

For a time, it used 5 million volts of electricity to shoot hydrogen nuclei down a vacuum tube at up to 100 million miles an hour.

From The Wall Street Journal • Oct. 7, 2025

It accelerates electrons within a long vacuum tube to high energy and near–light-speed, while magnets steer them around the ring.

From Science Magazine • May 3, 2023

To measure this force within their vacuum tube, the researchers will suspend two samples made of different materials from a two-meter-tall, 1.50-meter-wide balance and induce the Casimir effect within one.

From Scientific American • Apr. 29, 2023

Dr. Ashkin worked at a Columbia University laboratory during World War II, developing a magnetron — a vacuum tube that generates microwaves — as part of an Army radar program.

From Washington Post • Sep. 28, 2020

At first I thought the radio’s vacuum tube had blown, but then a man’s voice came on the radio.

From "Prisoner B-3087" by Alan Gratz