The term imbecile was once used by psychiatrists to denote a category of people with moderate to severe intellectual disability, as well as a type of criminal.
[4] In the obsolete medical classification (ICD-9, 1977), these people were said to have "moderate mental retardation" or "moderate mental subnormality" with IQ of 35–49, as they are usually capable of some degree of communication, guarding themselves against danger and performing simple mechanical tasks under supervision.
[9][10] "Imbecile" as a concrete classification was popularized by psychologist Henry H. Goddard[11] and was used in 1927 by United States Supreme Court Justice Oliver Wendell Holmes Jr. in his ruling in the forced-sterilization case Buck v. Bell, 274 U.S. 200 (1927).
It fell out of professional use in the 20th century in favor of mental retardation.
This had occurred with the earlier synonyms (for example, moron, imbecile, cretin, and idiot, formerly used as scientific terms in the early 20th century).