1. North American blackbird that follows cattle and lays eggs in other birds' nests;
The Collaborative International Dictionary of English v.0.48:
Cowbird \Cow"bird`\ (-b[~e]rd`), n. (Zool.)
The cow blackbird (Molothrus ater), an American starling.
Like the European cuckoo, it builds no nest, but lays its
eggs in the nests of other birds; -- so called because
frequently associated with cattle.
WordNet (r) 3.0 (2006):
n 1: North American blackbird that follows cattle and lays eggs
in other birds' nests