Pronunciation: lū′men, -min-ă, -menz
1. The space in the interior of a hollow tubular structure (artery or intestine).
2. The unit of luminous flux; the luminous flux emitted in a unit solid angle of 1 steradian by a uniform point source of light having a luminous intensity of 1 candela.
3. The volume enclosed within the membranes of a mitochondrion or of the endoplasmic reticulum.
4. The bore of a catheter or hollow needle.
The definition information for lumen is provided by Stedman's. You can search our medical dictionary here.
Stedman's, part of Lippincott Williams & Wilkins, provides a comprehensive line of health-science publications for healthcare professionals and medical students.