World English Dictionary
lumen (ˈluːmɪn)
n , pl -mens, -mina
1.  lm the derived SI unit of luminous flux; the flux emitted in a solid angle of 1 steradian by a point source having a uniform intensity of 1 candela
2.  anatomy a passage, duct, or cavity in a tubular organ
3.  a cavity within a plant cell enclosed by the cell walls
[C19: New Latin, from Latin: light, aperture]

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

proper name of phenobarbitone, from 1912.
Online Etymology Dictionary, © 2010 Douglas Harper
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