Retarded is a word to describe someone who is mentally slow. This is a medical word that spread to slang, and is today considered very insulting and inappropriate.

Some uses of retarded are harmless, like if you said wearing a backpack retarded or slowed down your progress on a hike. However, if you use retarded to mean stupid, you're on dangerous ground. Out of respect for people who have clinical mental retardation, this is considered an offensive term to throw around.

Definitions of retarded

adj relatively slow in mental or emotional or physical development

“providing a secure and sometimes happy life for the retarded
stupid, unintelligent
lacking intelligence
backward, feebleminded, half-witted, slow-witted
retarded in intellectual development
idiotic, imbecile, imbecilic
having a mental age of three to seven years
having a mental age of between eight and twelve years
afflicted with cretinism
not as far along as normal in development
dim-witted, simple, simple-minded
lacking mental capacity and subtlety
characterized by or characteristic of exceptionally early development or maturity (especially in mental aptitude)
having the capacity for thought and reason especially to a high degree
farther along in physical or mental development
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n people collectively who are mentally retarded

“he started a school for the retarded
developmentally challenged, mentally retarded
Type of:
(plural) any group of human beings (men or women or children) collectively

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