出典:Wiktionary
mental retardation (uncountable)
This term is no longer an accepted medical term in the United States. In September 2013, the Federal Register, under the agency of the The United States Social Security Administration (SSA), changed its guidelines and replaced "mental retardation" with "intellectual disability", due to the negative connotations and offensive nature of the word retardation, meaning "delay" or "hindrance", and the common use of retard and retarded as pejoratives.