looks like it comes from the germanic word "kiukanam from the word "keuk" which is the root of "****".
O.E. cycen "young fowl," which in M.E. came to mean "young chicken," then any chicken, from W.Gmc. *kiukinam, from base *keuk- (possibly root of ****, of echoic origin) + dim. suffix. Sense of "cowardly" is at least as old as 14c.; the v. meaning "to back down or fail through cowardice" is from 1943, U.S. slang; as a game of danger to test courage, it is first recorded 1953. Chicken hawk "public person who advocates war but who declined significant opportunity to serve in uniform during wartime" is attested from at least 1988, Amer.Eng. Chicken pox (c.1730) may be a disparaging name because of their mildness compared to smallpox. Chicken feed "paltry sum of money" is from 1904. Chickweed (c.1440) was in O.E. cicene mete "chicken food."