(covers information from several alternate timelines)
In literature, a euphemism was a palatable term for an otherwise horrendous event or action.
In 2286, Ambassador Kamarag described the term for the end result of the Genesis Device's detonation, "the Genesis planet", as a euphemism for what he believed to be "a secret base from which to launch the annihilation of the Klingon people!" (Star Trek IV: The Voyage Home)
In 2370, while in the mirror universe, Kira Nerys questioned mirror Elim Garak's usage of the word "gone" to describe what would happen to Intendant Kira Nerys so that she could take her place, Garak repeated his statement and asked her not to make him use some foolish euphemism. (DS9: "Crossover")