say it: ri-TAHR-did
retarded is a noun and adjective meaning "people collectively who are mentally retarded". It carries 2 recorded senses.
relatively slow in mental or emotional or physical development
“providing a secure and sometimes happy life for the retarded”
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for retarded come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.