1. the substitution of a harsh, disparaging, or unpleasant expression for a more neutral one.
2. an expression so substituted.
They were given considerable latitude in determining who should become a target of their “collection efforts.” (The term “spying” was considered a dysphemism, though many believed it to be a more honest description of domestic intelligence work.)
— David Lindsey, An Absence of Light, 1994
Dysphemism is derived from the Greek dys- meaning “ill, bad” and phḗmē meaning “speaking.” It entered English in the late 1800s.