cakewalk

From cake + walk. Originally an African-American form of dance and music that developed after the Civil War, later popularised by minstrel shows. It was danced at social events, with the best dancers often receiving cake as a prize. It derives from dance competitions by plantation slaves in which the style of dance lampooned the ballroom dances of the slaveowners. Slaveowners seem to have found the competitions entertaining and the habit of offering cake may originate from this period. The name is sometimes also applied to the dance's precursor on the plantations. Doing the cakewalk well required virtuosity, and a major aesthetic aspect of that virtuosity was the apparent ease with which the dance was performed. This gave rise to the idiom as easy as a cakewalk, which in turn led to the sense of cakewalk as something that is easy. See the linked Wikipedia article for more.

来源：wiktionary