Chicken is a synonym of coward.
As nouns the difference between coward and chicken
is that
coward is a person who lacks courage while
chicken is (countable) a domestic fowl,
gallus gallus , especially when young.
As adjectives the difference between coward and chicken
is that
coward is cowardly while
chicken is cowardly.
As a verb chicken is
to avoid as a result of fear.