something that causes or entails suffering; "I cannot think it a hardship that more indulgence is allowed to men than to women"- James Boswell; "the many hardships of frontier life"
a cavity or passage in a tubular organ; "the lumen of the intestine"
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