adult male chicken, especially in North America. Originated in the 18th century, possibly as a euphemism to avoid the sexual connotation of the word cock.
* Yardbird: a chicken (southern United States, dialectal)

Chicken can mean a chick, and this was historically the meaning of the word chicken, as in William Shakespeare's play Macbeth, where Macduff laments the death of "all my pretty chickens and their dam".