"retardation" in the noun sense
1. deceleration, slowing, retardation
a decrease in rate of change
"the deceleration of the arms race"
the extent to which something is delayed or held back
3. retardant, retardent, retardation
any agent that retards or delays or hinders
4. retardation, mental retardation, backwardness, slowness, subnormality
lack of normal development of intellectual capacities
5. slowdown, lag, retardation
the act of slowing down or falling behind
Source: WordNet® (An amazing lexical database of English)
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