\H[ae]m`a*cy"a*nin\, n. [H[ae]ma- + Gr.? a dark blue
substance.] (Physiol. Chem.)
A substance found in the blood of the octopus, which gives to
it its blue color.
Note: When deprived of oxygen it is colorless, but becomes
      quickly blue in contact with oxygen, and is then
      generally called oxyh[ae]macyanin. A similar blue
      coloring matter has been detected in small quantity in
      the blood of other animals and in the bile.