The Collaborative International Dictionary of English v.0.48:
Muskrat \Musk"rat`\, n.
1. (Zool.) A North American aquatic fur-bearing rodent
(Ondatra zibethica formerly Fiber zibethicus). It
resembles a rat in color and having a long scaly tail, but
the tail is compressed, the hind feet are webbed, and the
ears are concealed in the fur. It has scent glands which
secrete a substance having a strong odor of musk. Called
also musquash, musk beaver, ondatra, and sometimes
[1913 Webster +PJC]
2. (Zool.) The musk shrew.
3. (Zool.) The desman.