retardation

From 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. (psychology, dated, offensive) Ellipsis of mental retardation.
   • 2014, The Eric Andre Show, season 3, episode 6, Eric Andre (actor):

     Me and my friends used to feed LSD to this little retarded girl in our neighborhood and we'd lock arms around her and go "nightmare! Nightmare! Nightmare! Nightmare! Nightmare! Nightmare! Nightmare! Nightmare!" It actually cured her retardation.

4. (colloquial, derogatory, offensive) Extreme stupidity.
5. That which retards; an obstacle; an obstruction.
6. (physics) Deceleration; reduction in the magnitude of velocity.
   • 1960 April, “The braking of trains”, in Trains Illustrated, page 237:

     [...] the effect is automatically to select a braking force which is higher at above 40 m.p.h., in the initial stages of retardation, but is reduced as the speed falls below 40 m.p.h.

7. (music) A suspension which resolves upwards.

• growth retardation
• mental retardation

• “retardation”, in The Century Dictionary […], New York, N.Y.: The Century Co., 1911, →OCLC.
• “retardation”, in Webster’s Revised Unabridged Dictionary, Springfield, Mass.: G. & C. Merriam, 1913, →OCLC.