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
suddenly and unexpectedly; "rain caught them unawares"; "sorrow comes to all, and to the young it comes with bittered agony because it takes them unawares"- A.Lincoln
without forethought or plan; inadvertently; "came upon the diamond unawares"
a device for showing the operating condition of some system
a signal for attracting attention
(chemistry) a substance that changes color to indicate the presence of some ion or substance; can be used to indicate the completion of a chemical reaction or (in medicine) to test for a particular reaction