The Collaborative International Dictionary of English v.0.48:

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).
   [1913 Webster]

WordNet (r) 3.0 (2006):

pyocyanin
    n 1: a toxic blue crystalline antibiotic found in green pus