Etymology
retard (v.)

late 15c., retarden, "make slow or slower; keep back, hinder, delay" (transitive), from French retarder "restrain, hold (someone) back, keep (someone from doing something); come to a stop" (13c.) and directly from Latin retardare "make slow, delay, keep back, hinder" (see retardation). Related: Retarded; retarding. The intransitive sense of "be delayed" is from 1640s. 

The noun retard is recorded from 1788 in the sense "retardation, delay;" from 1970 in the offensive meaning "retarded person," originally American English, with accent on first syllable. Other words used for "one who is mentally retarded" include retardate (1956, from Latin retardatus), and U.S. newspapers 1950s-60s often used retardee (1950).

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retarder (n.)

1640s, "one who or that which checks or delays," agent noun from retard (v.). Scientific sense of "substance which slows down a reaction" by 1878. Specifically of braking mechanisms by 1937, originally on railroad cars.

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retardance (n.)

1550s, "slowness, a making slower, retardation," from French retardance, from retarder (see retard (v.)). It seems to persist in reference to resistance to fire, in which sense it dates from 1921. Related: Retardancy.

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retardant (adj.)

"tending to hinder," 1640s, from retard (v.) + -ant or from Latin retardantem (nominative retardans), present participle of retardare. From 1867 as a noun, "retardant substance, substance that inhibits some phenomenon or process."

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retarded (adj.)

1810, "delayed," past-participle adjective from retard (v.). In childhood development psychology, "mentally slow, lagging significantly in mental or educational progress," especially if due to some impairment, attested from 1895 (G.E. Shuttleworth, "late medical superintendent, Royal Albert Asylum, for idiots and imbeciles of the northern counties, Lancaster," perhaps inspired by Italian tardivi). Its application has shifted over the years based on what the progress or lack of it was measured against (peers, a score on IQ tests, etc.), but the progress gap was deemed "significant."

Fashions in labeling this group change almost from year to year; in the 1960s, mental retardation was the favorite appellation, and justifiably so in that it does not imply that inheritance or constitutional defects are always the cause of mental retardation. ["Campbell's Psychiatric Dictionary," 2004]
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tarry (v.)
early 14c., "to delay, retard" (transitive), of uncertain origin. Some suggest a connection to Latin tardare "to delay," or Old English tergan, tirgan "to vex, irritate, exasperate, provoke," which yielded a Middle English verb identical in form to this one. Intransitive meaning "to linger" is attested from late 14c. Related: Tarried; tarrying; tarrysome.
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damp (v.)

late 14c., "to suffocate" (with or as with damp, foul air in a mine), from damp (n.). Figurative meaning "to check or retard the force or action of (the spirits, etc.)" is attested by 1540s. Meaning "to moisten" is recorded from 1670s. Century Dictionary (1897) states that "Dampen is now more common in the literal sense, and is sometimes used in the derived senses." Related: Damped; damping.

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demurrage (n.)

"any detention of a vessel by the freighter in loading or unloading beyond the time originally stipulated" [Century Dictionary], 1640s, from Old French demorage, from demorer "to stay, delay, retard," from Latin demorari "to linger, loiter, tarry," from de- (see de-) + morari "to delay," from mora "a pause, delay" (see moratorium). Also "a payment in compensation by the freighter for such a delay."

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slake (v.)
late Old English sleacian, slacian "become slack or remiss; slacken an effort" (intransitive); "delay, retard" (transitive), from slæc "lax" (see slack (adj.)). Transitive sense of "make slack" is from late 12c. Sense of "allay, diminish in force, quench, extinguish" (in reference to thirst, hunger, desire, wrath, etc.) first recorded early 14c. via notion of "make slack or inactive." Related: Slaked; slaking.
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demurrer (n.)

1530s, "a pause, a delay" (a sense now obsolete); 1540 as legal pleading to the effect that, even conceding the facts to be as alleged by the opponent, he is not entitled to legal relief, from Anglo-French demurrer, Old French demorer "to delay, retard," from Latin demorari "to linger, loiter, tarry," from de- (see de-) + morari "to delay," from mora "a pause, delay" (see moratorium). Transferred sense of "objection raised or exception taken" to anything is by 1590s.

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