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lu·men

(lmən)

n. pl. lu·mens or lu·mi·na (-mə-nə)

1. Anatomy The inner open space or cavity of a tubular organ, as of a blood vessel or an intestine.

2. Biology The interior of a membrane-bound compartment or organelle in a cell.

3. Abbr. lm Physics The SI unit of luminous flux, equal to the amount of light per unit time passing through a solid angle of one steradian from a light source of one candela intensity radiating equally in all directions. See Table at measurement.

[Latin lūmen, an opening, light; see leuk- in the Appendix of Indo-European roots.]

lumen·al, lumin·al adj.

Indo-European & Semitic Roots Appendices

Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:

Indo-European Roots

Semitic Roots

The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.

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