What is the meaning of the word "haem"?

Definitions:

A biological term referring to a crucial component of hemoglobin, the protein in red blood cells that carries oxygen throughout the body. NOUN
- Disorders in haem production can lead to anemia and other metabolic complications.
A complex red organic pigment containing iron and other atoms to which oxygen binds. NOUN
- The iron in haem enables red blood cells to transport oxygen efficiently throughout the body.
An iron-containing molecule that binds oxygen, giving blood its red color. NOUN
- Haem in myogobin gives muscle tissue its characteristic red color.