“Retarded” used to be a polite word; it was introduced to replace “idiot,” “imbecile,” and “moron,” which had once, themselves, been polite terms. Linguists call this process the “euphemism treadmill.” Ironically, to use “retarded” as a way of disparaging a person or idea is more offensive than to use “imbecilic” or “moronic”: terms ditched—for being too offensive—in favor of “retarded.” This lexical switch obviously has not succeeded in the long term. When White House Chief of Staff Rahm Emanuel in a 2009 strategy meeting dubbed a proposal that displeased him “retarded,” it prompted calls among prominent Republicans for his resignation, and (in lieu of resignation) a personal apology to the chairman of the Special Olympics. In May of 2010, the Senate’s Health, Education, Labor, and Pensions Committee approved a bill called Rosa’s Law that would strike “retarded” from all federal language, replacing it with “intellectually disabled.” The treadmill continues.

Brian Christian, The Most Human Human: What Artificial Intelligence Teaches Us About Being Alive (2011)