The chicken is well-represented in slang, punching, at least linguistically, well above its diminutive weight. That said, it is the stereotypes of size and vulnerability that determine its meanings, though its perceived 'perkiness' also plays a role, notably in the nickname of the bareknuckle prizefighter Henry or 'Hen' Pearce (1707-1809), known as 'The Game Chicken'.
The primary uses, however, remain those that suggest weakness. Thus the early use to mean a girl or woman, which would become the more recent chick.
The first example we have of chicken meaning a coward comes in 1600: William Kemp's Nine Days' Wonder: "It did him good to have ill words of a hoddy doddy! a hebber de hoy!, a chicken! a squib."
The equation stuck. Typically, here:
Dickens, Martin Chuzzlewit (1844): "Why, what a chicken you are! You are not afraid of being robbed, are you?"
From a coward one moves on to a weak or naïve person:
W Godwin, Caleb Williams (1794): "You are not such a chicken as to suppose, if so be as you are innocent, that that will make your game altogether sure."
Adjectives meaning cowardly can be found in compounds, the first of which, chicken-hearted, seem to be the earliest example of the equation on record (although this chicken began life as a hen):
Skelton, Why Come Ye Nat to Courte? (1522): "They kepe them in theyr holdes Lyke hen-herted cokoldes."
T Betterton, Match in Newgate (1680): "Was there ever such a chicken-hearted Son of a Whore?"
There is also chicken-livered: Westmoreland Gazette (5 Sept, 1835): "A hen-pecked husband, forsooth! [...] the veriest chicken-livered husband in existence."
And the term is especially well-known in the phrase to play chicken, a contest of nerve in which two cars drive towards either each other or an obstacle, cliff edge, etc – the loser being the driver who turns aside first; thus any form of foolish dare-devilry.
FL Allen, "The Changes It Wrought" in Brookhouser, These Were Our Years (1952): "Youngsters had learned to play 'chicken' and hot-rod enthusiasts had taken to the road."
Adjectivally, one could already find chicken meaning cowardly in the 1920s, here used in a piece of fiction writen a decade later:
JT Farrell, Judgment Day (1935; context 1920s): "He was [...] so chicken."
Finally, and again emerging from the juvenile delinquents, there is chicken-gutted or chicken-gut:
H Ellison, Web of the City (1958): "They had never been chickengut while he was top man."
Jonathon Green, author of 'Green's Dictionary of Slang'
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