Usra is the Bear Star

So when a friend was asking for a four letter word meaning "Bear Star", I came up with Osos. Working the puzzle more, she found that the Bear Star is actually Ursa. In confirming this information online, I found that, " The constellation Ursa Major contains the group of stars commonly called the Big Dipper. The handle of the Dipper is the Great Bear's tail and the Dipper's cup is the Bear's flank. The Big Dipper is not a constellation itself, but an asterism, which is a distinctive group of stars. Another famous asterism is the Little Dipper in the constellation Ursa Minor."