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")
1.
Explanation of the lumen cinereum in the moon. - from The Notebooks of Leonardo Da Vinci, Complete by Leonardo Da Vinci