Relating to or produced by a cathode, the negative electrode in an electrical device.
From cathode (Greek kata- 'down' + hodos 'path') plus -al (forming adjectives). The term became common in physics and electrochemistry in the 19th century.
Cathodal rays were actually electron beams—when scientists discovered them in the 1800s, they didn't know what they were shooting from cathodes, but those 'mystery rays' led directly to discovering electrons!
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