Nouns

(n)deceleration, slowing, retardationa decrease in rate of change“the deceleration of the arms race”
(n)retardationthe extent to which something is delayed or held back
(n)retardant, retardent, retardationany agent that retards or delays or hinders“flame-retardant”
(n)retardation, mental retardation, backwardness, slowness, subnormalitylack of normal development of intellectual capacities
(n)slowdown, lag, retardationthe act of slowing down or falling behind