Usage note In reference to low intellectual ability, the terms retarded, retardation, and mental retardation are now usually perceived as insulting. There are several acceptable alternatives. In general, someone with a mental, physical, or emotional disability may be described as developmentally disabled, or as a person with a developmental disability. If it is specifically a mental disability, the person may be described as cognitively impaired or intellectually (or mentally) disabled. Such a person may be referred to as an individual with a cognitive impairment or a person with an intellectual (or mental) disability. The slang term retard is a term of abuse used especially by children, though much less commonly than in the past. In both of its meanings, retard is perceived as insulting to disabled people. See also cripple.
late 15c., from Fr. retarder (13c.), from L. retardare (see retardation). The noun is recorded from 1788 in the sense "retardation, delay;" from 1970 in offensive meaning "retarded person," originally Amer.Eng., with accent on first syllable
1810, pp. adj. from retard. In childhood development sense, "mentally slow," attested from 1895 (cf. It. tardivi).