–noun, plural ducks, ( especially collectively for 1, 2 ) duck.
1. any of numerous wild or domesticated web-footed swimming birds of the family Anatidae, esp. of the genus Anas and allied genera, characterized by abroad, flat bill, short legs, and depressed body.
2. the female of this bird, as distinguished from the male. Compare drake1 .
water off a duck’s back, something that has little or no effect: Our criticisms of his talk rolled off him like water off a duck’s back.
World English Dictionary
— n , pl ducks , duck
1. any of various small aquatic birds of the family Anatidae, typically having short legs, webbed feet, and a broad blunt bill: order Anseriformes
2. the flesh of this bird, used as food
3. the female of such a bird, as opposed to the male (drake)
4. any other bird of the family Anatidae, including geese, and swans
8. informal like water off a duck’s back without effect
9. informal take to something like a duck to water to become adept at or attracted to something very quickly
* Above definitions from Dictionary.com