Real Dictionary

bird
countable noun: A bird is a creature with feathers and wings. Female birds lay eggs. Most birds can fly.
countable noun: Some people refer to young women as birds. This use could cause offence.

bird in American English
any of a class (Aves) of warmblooded, two-legged, egg-laying vertebrates with feathers and wings
to shoot or catch birds
noun: any warm-blooded vertebrate of the class Aves, having a body covered with feathers, forelimbs modified into wings, scaly legs, a beak, and no teeth, and bearing young in a hard-shelled egg

bird in British English
noun
noun: any warm-blooded egg-laying vertebrate of the class Aves, characterized by a body covering of feathers and forelimbs modified as wings. Birds vary in size between the ostrich and the humming bird