DuckCorp Dico

Found one definition

1.                 From WordNet (r) 3.0 (2006):
                   
   
   
                   
                     
   lumen
       n 1: 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 [syn: lumen, lm]
       2: a cavity or passage in a tubular organ; "the lumen of the
          intestine"