"the young of the domestic hen," also of some other birds, mid-14c., probably originally a shortening of chicken (n.).
Extended 14c. to human offspring, "person of tender years" (often in alliterative pairing chick and child) and thence used as a term of endearment. As slang for "young woman" it is first recorded 1927 (in "Elmer Gantry"), supposedly from African-American vernacular. In British use in this sense by c. 1940; popularized by Beatniks late 1950s (chicken in this sense is by 1860). Sometimes c. 1600-1900 chicken was taken as a plural, chick as a singular (compare child/children) for the domestic fowl.