retardation

an act or instance of retarding

the extent to which something is retarded

a musical suspension; specifically : one that resolves upward

mild to severe impairment in intellectual ability equivalent to an IQ of 70 to 75 or below that is accompanied by significant limitations in social, practical, and conceptual skills (as in interpersonal communication, reasoning, or self-care) necessary for independent daily functioning and that has an onset before age 18 : intellectual, disability