1810, "delayed," past-participle adjective from retard (v.). In childhood development sense, "mentally slow," attested from 1895 (perhaps inspired by Italian tardivi).
he started a school for the retarded
providing a secure and sometimes happy life for the retarded
retaliatory
retard
retardance
retardant
retardation
retarded
retarder
retch
rete
retell
retention
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