people collectively who are mentally retarded
"he started a school for the retarded"
simple past tense and past participle of retard
"The delayed shipment arrived two weeks later than expected because it was retarded by heavy snow in the mountains."
relatively slow in mental or emotional or physical development
"providing a secure and sometimes happy life for the retarded"
Delayed; delayed in development, hindered; impeded.
"The traffic was retarded by a sudden accident on the highway."