'Photon' was coined by Gilbert Lewis in 1926 — Greek 'phos' (light) + the particle suffix '-on.'
A quantum of electromagnetic radiation, the fundamental particle of light, having zero rest mass and carrying energy proportional to its frequency.
From Greek 'phōs' / 'phōtos' (light, genitive of 'phōs'), from PIE *bʰeh₂- (to shine, to gleam). The PIE root *bʰeh₂- is one of the primary light-roots in the family: Sanskrit 'bhāti' (shines), Greek 'phainein' (to show, to bring to light → 'phenomenon', 'fantasy'), Latin 'fari' (to speak — the idea that words 'illuminate' or 'bring to light'), Old English 'bēacn' (beacon — a shining signal). The technical term 'photon' was coined in 1926 by American physicist Gilbert N. Lewis, who
Gilbert Lewis coined 'photon' in a 1926 letter to Nature, but his theoretical concept of the photon was actually wrong — he imagined photons as being conserved (neither created nor destroyed), which is not the case. The word stuck anyway because physicists needed a convenient name for Einstein's 'light quantum,' and Lewis's coinage was perfectly formed from the Greek.
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