retardation

(noun) a decrease in rate of change. Synonyms: deceleration, slowing. Example: "The deceleration of the arms race."

(noun) the extent to which something is delayed or held back.

(noun) any agent that retards or delays or hinders. Synonyms: retardant, retardent. Example: "Flame-retardant."

(noun) lack of normal development of intellectual capacities. Synonyms: mental retardation, backwardness, slowness, subnormality.

(noun) the act of slowing down or falling behind. Synonyms: slowdown, lag.