retardation

retard +‎ -ation

retardation (countable and uncountable, plural retardations)

1. The act of retarding or delaying; hindrance.
   1. (acoustics) The distance by which one wave is behind another.
   2. (music) The act of diminishing the rate of speed.
   3. (telegraphy) A decrease in the speed of telegraph signalling.
2. The extent to which anything is retarded; the result of any retarding or delay; mental, social, or physical slowness.
3. (colloquial, derogatory, offensive) Extreme stupidity.
4. That which retards; an obstacle; an obstruction.
5. (physics) Deceleration; reduction in the magnitude of velocity.
6. (music) A suspension which resolves upwards.

• retardation in The Century Dictionary, New York, N.Y.: The Century Co., 1911.
• retardation in Webster’s Revised Unabridged Dictionary, G. & C. Merriam, 1913.