Etymology
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conversion (n.)

mid-14c., originally of religion, "a radical and complete change in spirit, purpose, and direction of life away from sin and toward love of God," from Old French conversion "change, transformation, entry into religious life; way of life, behavior; dwelling, residence; sexual intercourse," from Latin conversionem (nominative conversio) "a turning round, revolving; alteration, change," noun of action from past-participle stem of convertere "to turn around; to transform," from assimilated form of com "with, together" (see con-) + vertere "to turn" (from PIE root *wer- (2) "to turn, bend").

Sense of "a change from one religion to another" (especially to Christianity) is from c. 1400 in English. General sense of "transformation, a turning or changing from one state to another" is from early 15c. In reference to the use of a building, from 1921. Conversion disorder "hysteria" (attested from 1946 but said to have been coined by Freud) was in DSM-IV (1994). Conversion therapy in reference to homosexuality is by 1979.

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reaction (n.)

"action in resistance or response to another action or power," 1640s, from re- "back, again, anew" + action (q.v.). Modeled on French réaction, older Italian reattione, from Medieval Latin reactionem (nominative reactio), a noun of action formed in Late Latin from the past-participle stem of Latin reagere "react," from re- "back" + agere "to do, perform."

Originally a word in physics and dynamics. In chemistry, "mutual or reciprocal action of chemical agents upon each other," by 1836. The general sense of "action or feeling in response" (to a statement, event, etc.) is recorded from 1914. Reaction time, "time elapsing between the action of an external stimulus and the giving of a signal in reply," attested by 1874.

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reactionary (adj.)

1831, "of or pertaining to political reaction, tending to revert from a more to a less advanced policy," on model of French réactionnaire (19c.), from réaction (see reaction). In Marxist use by 1858 as "tending toward reversing existing tendencies," opposed to revolutionary and used opprobriously in reference to opponents of communism. Non-political use, "of or pertaining to a (chemical, etc.) reaction" (1847) is rare. As a noun, "person considered reactionary," especially in politics, one who seeks to check or undo political action, by 1855.

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reactive (adj.)

1712, "repercussive, echoing," a sense now obsolete, from react + -ive. By 1822 as "caused by a reaction;" 1888 as "susceptible to (chemical) reaction." Related: Reactively; reactiveness; reactivity.

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palatalization (n.)

"conversion into palatal sounds," 1863, from palatal. Related: Palatalize (1851);palatalized; palatalizing.

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dramatization (n.)

"a dramatic representation; conversion into drama," 1796, from dramatize + noun ending -ation.

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saponification (n.)

"conversion into soap," 1801, from French saponification, from saponifier, from Modern Latin saponificare, from sapon "soap" (see soap (n.)) + -ficare, combining form of Latin facere "to make" (from PIE root *dhe- "to set, put").

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anaphylaxis (n.)
"severe allergic reaction," 1905, from Latin anaphylaxis, perhaps based on French anaphylaxie (1902); see anaphylactic.
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double-take (n.)

"exaggerated reaction to surprise," 1922, from double (adj.) + take (n.). Originally in stage comedy acting.

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Intifada (n.)
"Palestinian revolt," 1985, from Arabic, literally "a jumping up" (in reaction to something), from the verb intafada "to be shaken, shake oneself."
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