noun

1. the red coloring matter of the red blood corpuscles of vertebrates, a protein yielding heme and globin on hydrolysis: it carries oxygen from the lungs to the tissues, and carbon dioxide from the tissues to the lungs
2. any of various respiratory pigments found in the blood or muscle tissue of many invertebrates and in the root nodules of some plants

Etymology: contr. (as if < hemo-) < earlier haematoglobulin: see hemato- & globulin