(1) The use of an agreeable or inoffensive word or expression for one that may offend or disgust. (2) An expression used in this way.
Example:
The Victorians, uncomfortable with the physical side of human existence, had euphemisms for most bodily functions.
Euphemism is an ancient part of the English language. While particular expressions come into and go out of vogue, the need for euphemism remains constant. Golly and gosh started out as euphemisms for God, and darn is a familiar euphemism for damn. Shoot, shucks, and sugar are all euphemistic substitutes for a well-known vulgar word. The standard household bathroom fixture has given rise to host of euphemistic substitutes, including convenience, head, john, potty, privy, and water closet.