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Added 10 October 2026

lumen

/ˈluːmən/ noun

Latin root: lūmen Wiktionary

noun Definition from Wiktionary (CC BY-SA). Pronunciation from Wiktionary, via Kaikki.org. More about lumen at Wordnik → Where our words come from →

In the International System of Units, the derived unit of luminous flux; the light that is emitted in a solid angle of one steradian from a source of one candela. Symbol: lm.
The cavity or channel within a tube or tubular organ.
The cavity bounded by a plant cell wall.

Origin

Borrowed from Latin lūmen (“light, an opening”). Use as a unit was first adopted by French physicist André Blondel in 1894.

From Wiktionary, via Kaikki.org (CC BY-SA)

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