"lumen" in the noun sense
1. lumen, lm
a unit of luminous flux equal to the amount of light given out through a solid angle of 1 steradian by a point source of 1 candela intensity radiating uniformly in all directions
2. lumen
a cavity or passage in a tubular organ
"the lumen of the intestine"
Source: WordNet® (An amazing lexical database of English)
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