Main Entry: lu·men

Pronunciation: \ˈlü-mən\

Function: noun

Inflected Form(s): plural lu·mi·na \-mə-nə\ or lumens

1 : the cavity of a tubular organ or part <the lumen of a blood vessel>
2 : the bore of a tube (as of a hollow needle or catheter)
3 : a unit of luminous flux equal to the light emitted in a steradian by a uniform point source of one candle intensity