Is it ensure, insure, or assure?
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.
An agreeable word or expression substituted for one that is potentially offensive, often having to do with bodily functions, sex, or death; for example, rest room for toilet, lady of the evening for prostitute. The Nazis used euphemism in referring to their plan to murder the world's Jews as “the Final Solution.”