retardation

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The act or process of delaying or impeding.
• noun The condition of being delayed or impeded.
• noun The extent to which something is held back or delayed.
• noun Something that retards; a delay or hindrance.
• noun Often Offensive Impaired intellectual development.
• noun Music A diminishing of tempo; a retard.

from The Century Dictionary.

• noun The act of retarding or making slower, or its effect; the hindering of motion, growth, or progress, or the hindrance effected; the act of delaying or impeding.
• noun In physics:
• noun A continuous decrement of velocity; a negative acceleration.
• noun In acoustics and optics, the distance by which one wave is behind another. Better called retard, being translation of French retard.
• noun Postponement; deferment.
• noun Specifically, in music:
• noun The act, process, or result of diminishing the speed or pace of the tempo
• noun The prolongation of a concordant tone into a chord where it is a discord which is resolved upward: opposed to anticipation, and distinguished from suspension by the upward resolution
• noun In telegraphy, decrease in the speed of telegraph-signaling due to self-induction and induction from surrounding conductors.
• noun That which retards; a hindrance; an obstruction; an impediment.

from the GNU version of the Collaborative International Dictionary of English.

• noun The act of retarding; hindrance; the act of delaying; ; -- opposed to acceleration.
• noun That which retards; an obstacle; an obstruction.
• noun (Mus.) The keeping back of an approaching consonant chord by prolonging one or more tones of a previous chord into the intermediate chord which follows; -- differing from suspension by resolving upwards instead of downwards.
• noun The extent to which anything is retarded; the amount of retarding or delay.
• noun The age of the tide; the retard of the tide. See under Retard, n.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The act of retarding or delaying; hindrance.
• noun The extent to which anything is retarded; the result of any retarding or delay; mental, social, or physical slowness.
• noun That which retards; an obstacle; an obstruction.
• noun physics Deceleration; reduction in the magnitude of velocity.
• noun music A suspension which resolves upwards.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a decrease in rate of change
• noun the extent to which something is delayed or held back
• noun any agent that retards or delays or hinders
• noun lack of normal development of intellectual capacities
• noun the act of slowing down or falling behind