Euphemism

A mild or indirect term substituted for one considered too harsh, blunt, or offensive. A polite way of referring to something unpleasant or taboo.

From Greek 'euphemismos,' combining 'eu' (good) and 'pheme' (speech). Literally means 'good speech' or 'speaking well.' Originally used in religious contexts to avoid directly naming gods or evil spirits that might be offended by direct reference.