zebra

noun

1. Any of three species of genus Equus: E. grevyi, E. quagga, or E. zebra, all with black and white stripes and native to Africa.
2. A referee.
3. An unlikely diagnosis, especially for symptoms probably caused by a common ailment. (Originates in the advice often given to medical students: "when you hear hoofbeats, think of horses, not zebras".)
4. A biracial person, specifically one born to a member of the Sub-Saharan African race and a Caucasian.