Retardedness (noun)
The state or condition of being retarded.
Retardation (noun)
The act of retarding or delaying; hindrance.
Retardation (noun)
The extent to which anything is retarded; the result of any retarding or delay; mental, social, or physical slowness.
Retardation (noun)
Extreme stupidity.
Retardation (noun)
That which retards; an obstacle; an obstruction.
Retardation (noun)
Deceleration; reduction in the magnitude of velocity.
Retardation (noun)
A suspension which resolves upwards.
Wiktionary