lu·men (lōō'mən) n.
pl.lu·mens or lu·mi·na (-mə-nə)
Anatomy The inner open space or cavity of a tubular organ, as of a blood vessel or an intestine.
Abbr. lmPhysics The unit of luminous flux in the International System, equal to the amount of light given out through a solid angle by a source of one candela intensity radiating equally in all directions. See Table at measurement.
Botany The cavity bounded by a plant cell wall.
[Latin lūmen, an opening, light; see leuk- in Indo-European roots.] lu'men·al, lu'min·al adj.
(lōō'mən) 