What does "moccasin" mean?

Moccasin: (Zoöl.) A poisonous snake of the Southern United States. The water moccasin (Ancistrodon piscivorus) is usually found in or near water. Above, it is olive brown, barred with black; beneath, it is brownish yellow, mottled with darker. The upland moccasin is Ancistrodon atrofuscus. They resemble rattlesnakes, but are without rattles. Moccasin flower (Bot.), a species of lady's slipper (Cypripedium acaule) found in North America. The lower petal is two inches long, and forms a rose-colored moccasin-shaped pouch. It grows in rich woods under coniferous trees.