Cocky comes from cock 'rooster' + -y, alluding to the strutting, self-assertive manner of a cockerel; attested in this sense from the 18th century. Morphologically, the surface form is analyzable into prefixes, suffixes, compounds, or participial endings that carry part of the history. The later sense follows a semantic development already present in the word's history. In modern use it means overly self-confident in a brash way. Derived formations include cockiness, cockily; related forms include cock.