chicken (n.) Look up chicken at Dictionary.com
Old English cicen (plural cicenu) "young fowl," which by early Middle English had came to mean "young chicken," then later any chicken, from Proto-Germanic *kiukinam (cognates: Middle Dutch kiekijen, Dutch kieken, Old Norse kjuklingr, Swedish kyckling, German Küken "chicken"), from root *keuk- (echoic of the bird's sound and possibly also the root of cock (n.1)) + diminutive suffixes.

Applied to the young of other bird species from early 13c. Adjective sense of "cowardly" is at least as old as 14c. (compare hen-herte "a chicken-hearted person," mid-15c.). As the name of a game of danger to test courage, it is first recorded 1953. Chicken feed "paltry sum of money" is by 1897, American English slang; literal use (it is made from the from lowest quality of grain) by 1834. Chicken lobster "young lobster," is from c.1960s, American English, apparently from chicken in its sense of "young." Generic words for "chicken" in Indo-European tend to be extended uses of "hen" words, as hens are more numerous among domestic fowl, but occasionally they are from words for the young, as in English and in Latin pullus.
chicken (v.) Look up chicken at Dictionary.com
"to back down or fail through cowardice," 1943, U.S. slang, from chicken (n.), almost always with out (adv.).