- 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
--1 is a kind of luminous flux unit
- lumen - a cavity or passage in a tubular organ; "the lumen of the intestine"
--2 is a kind of cavity, bodily cavity, cavum