euphemism (n.) Look up euphemism at Dictionary.com
1650s, from Greek euphemismos "use of a favorable word in place of an inauspicious one," from euphemizein "speak with fair words, use words of good omen," from eu- "good" (see eu-) + pheme "speaking," from phanai "speak" (see fame (n.)).

In ancient Greece, the superstitious avoidance of words of ill-omen during religious ceremonies, or substitutions such as Eumenides "the Gracious Ones" for the Furies (see also Euxine). In English, a rhetorical term at first; broader sense of "choosing a less distasteful word or phrase than the one meant" is first attested 1793. Related: Euphemistic; euphemistically.