Melaena

from WordNet (r) 3.0 (2006)

melaena
    n 1: abnormally dark tarry feces containing blood (usually from
         gastrointestinal bleeding) [syn: {melena}, {melaena}]

from The Collaborative International Dictionary of English v.0.48

Melaena \Me*lae"na\, n. [NL., fr. Gr. me`las, m., me`laina, f.,
   black.] (Med.)
   A discharge from the bowels of black matter, consisting of
   altered blood.
   [1913 Webster]