chickweed (n.)

"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 modern slang for "young woman" it is recorded by 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.

"plant not valued for use or beauty," Old English weod, uueod "grass, herb, weed," from Proto-Germanic *weud- (source also of Old Saxon wiod, East Frisian wiud), of unknown origin. Also applied to trees that grow abundantly. Meaning "tobacco" is from c. 1600; that of "marijuana" is from 1920s. The chemical weed-killer is attested by 1885.