hemoglobin

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The iron-containing respiratory pigment in red blood cells of vertebrates, consisting of about 6 percent heme and 94 percent globin.

from The Century Dictionary.

• noun The red substance which forms about nine tenths of the dry constituents of the red bloodcorpuscles and serves as the carrier of oxygen in the circulation.

from the GNU version of the Collaborative International Dictionary of English.

• noun Same as hemoglobin.
• noun (Physiol.) The normal coloring matter of the red blood corpuscles of vertebrate animals. It is composed of hematin and globulin, and is also called hæmatoglobulin. In arterial blood, it is always combined with oxygen, and is then called oxyhemoglobin. It crystallizes under different forms from different animals, and when crystallized, is called hæmatocrystallin. See Blood crystal, under blood.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The iron-containing substance in red blood cells that transports oxygen from the lungs to the rest of the body; it consists of a protein (globulin), and haem (a porphyrin ring with an atom of iron at its centre).

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a hemoprotein composed of globin and heme that gives red blood cells their characteristic color; function primarily to transport oxygen from the lungs to the body tissues
• noun a hemoprotein composed of globin and heme that gives red blood cells their characteristic color; function primarily to transport oxygen from the lungs to the body tissues