Merriam-Webster's Collegiate® Dictionary, 11th Edition
CHICKEN
I. noun
Etymology: Middle English chiken, from Old English cicen young chicken; akin to Old English cocc cock
Date: 14th century
1. the common domestic fowl ( Gallus gallus ) especially when young, any of various birds or their young, a young woman,
3. coward , any of various contests in which the participants risk personal safety in order to see which one will give up first, petty details, a young male homosexual,
II. adjective
Date: 1941
1. scared , timid , cowardly ,
2. slang insistent on petty details of duty or discipline, petty , unimportant,
III. intransitive verb (chickened; chickening)
Date: 1943
to lose one's nerve