retardation

Short definition from Wiktionary

Noun

1. 1
   The act of retarding or delaying; hindrance: The distance by which one wave is behind another.
2. 2
   The act of retarding or delaying; hindrance: The act of diminishing the rate of speed.
3. 3
   The act of retarding or delaying; hindrance: A decrease in the speed of telegraph signalling.
4. 4
   The extent to which anything is retarded; the result of any retarding or delay; mental, social, or physical slowness.
5. 5
   Ellipsis of mental retardation.
6. 6
   Extreme stupidity.
7. 7
   That which retards; an obstacle; an obstruction.
8. 8
   Deceleration; reduction in the magnitude of velocity.
9. 9
   A suspension which resolves upwards.