You're right--my Webster's has a similar definition. But the English word was borrowed from French, where it does mean "duck."
As Chico might say, why a duck?
Yes, but it's an English word now, with a different meaning. Not all borrowed words retain their original meaning.
As an aside, in France, their humorous weekly newspaper is called "Le Canard Enchaîné" which literally means "the chained duck."