Source : Webster's Revised Unabridged Dictionary (1913)

Haemacyanin \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.