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the electrode or terminal by which current leaves an electrolytic cell, voltaic cell, battery, etc.
the positive terminal of a voltaic cell or battery.
the negative terminal, electrode, or element of an electron tube or electrolytic cell.
Historical Examples

He disconnected one of the room’s tube-lights and contacted with the cathode.
Wandl the Invader Raymond King Cummings

He applied the current, moving the anode and the cathode slowly.
The Silent Bullet Arthur B. Reeve

The tube is then exhausted until the cathode rays strike against the window.
Encyclopaedia Britannica, 11th Edition, Volume 6, Slice 8 Various

The cathode is preferably formed of the same metal which is to be obtained.
Scientific American Supplement, No. 433, April 19, 1884 Various

Next this we have a luminous position called the “negative glow” or the “third cathode layer.”
Encyclopaedia Britannica, 11th Edition, Volume 6, Slice 8 Various

Waving away that orange gas, he reached for the cathode and held it up.
Spawn of the Comet Harold Thompson Rich

The rays start from the cathode A, and pass through a slit in a solid brass rod B fitting tightly into the neck of the tube.
Encyclopaedia Britannica, 11th Edition, Volume 6, Slice 8 Various

This is melted in an iron pot which also serves as the cathode in the electrolysis.
An Elementary Study of Chemistry William McPherson

Unlike the cathode rays, they were not deflected by magnets; and neither did they seem to be reflected or refracted similarly.
Invention Bradley A. Fiske

These rays are called cathode rays because they come from the cathode of the tube.
Physics Willis Eugene Tower

noun
the negative electrode in an electrolytic cell; the electrode by which electrons enter a device from an external circuit
the negatively charged electron source in an electronic valve
the positive terminal of a primary cell
n.

1834, from Latinized form of Greek kathodos “a way down,” from kata- “down” (see cata-) + hodos “way” (see cede). Proposed by the Rev. William Whewell (1794-1866), English polymath, and published by English chemist and physicist Michael Faraday (1791-1867). So called from the path the electric current was supposed to take. Related: Cathodic; cathodal. Cathode ray first attested 1880, but the phenomenon known from 1859; cathode ray tube is from 1905.
cathode
(kāth’ōd’)

The negative electrode in an electrolytic cell, toward which positively charged particles are attracted. The cathode has a negative charge because it is connected to the negatively charged end of an external power supply.

The source of electrons in an electrical device, such as a vacuum tube or diode.

The positive electrode of a voltaic cell, such as a battery. The cathode gets its positive charge from the chemical reaction that happens inside the battery, not from an external source. Compare anode.