Source : Webster's Revised Unabridged Dictionary (1913)

Pyocyanin \Py`o*cy"a*nin\, n. [Gr. ? pus + ? dark blue.]
   (Physiol. (Chem.)
   A blue coloring matter found in the pus from old sores,
   supposed to be formed through the agency of a species of
   bacterium ({Bacillus pyocyaneus}).

Source : WordNet®

pyocyanin
     n : a toxic blue crystalline antibiotic found in green pus