Etymology
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contagion (n.)

late 14c., "a communicable disease; a harmful or corrupting influence," from Old French contagion and directly from Latin contagionem (nominative contagio) "a touching, contact," often in a bad sense, "a contact with something physically or morally unclean, contagion," from contingere "to touch," from assimilated form of com "with, together" (see con-) + tangere "to touch," from PIE root *tag- "to touch, handle." Meaning "infectious contact or communication" is from 1620s.

A distinction between contagion and infection is sometimes adopted, the former being limited to the transmission of disease by actual contact of the diseased part with a healthy absorbent or abraded surface, and the latter to transmission through the atmosphere by floating germs or miasmata. There are, however, cases of transmission which do not fall under either of these divisions, and there are some which fall under both. In common use no precise discrimination of the two words is attempted. [Century Dictionary, 1897]
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infection (n.)
late 14c., "infectious disease; contaminated condition;" from Old French infeccion "contamination, poisoning" (13c.) and directly from Late Latin infectionem (nominative infectio) "infection, contagion," noun of action from past participle stem of Latin inficere "to spoil, to stain" (see infect). Meaning "communication of disease by agency of air or water" (distinguished from contagion, which is body-to-body communication), is from 1540s.
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contagious (adj.)

late 14c., "contaminating or contaminated, containing contagion" (of air, water, etc.); "communicable" (of disease); also "morally corrupting," from Old French contagieus (Modern French contagieux) and directly from Late Latin contagiosus, from Latin contagio "a touching, contact," often in a bad sense, "a contact with something physically or morally unclean, contagion," from contingere "to touch," from assimilated form of com "with, together" (see con-) + tangere "to touch," from PIE root *tag- "to touch, handle." Figuratively applied to anything apt to spread from one to another (rumor, etc.) from 1650s. Related: Contagiously; contagiousness.

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acrophobia (n.)

"morbid fear of heights," 1887, medical Latin, from Greek akros "at the end, topmost" (from PIE root *ak- "be sharp, rise (out) to a point, pierce") + -phobia "fear." Coined by Italian physician Dr. Andrea Verga in a paper describing the condition, from which Verga himself suffered.

In this paper, read somewhat over a year ago at the congress of alienists at Pavia, the author makes confession of his own extreme dread of high places. Though fearless of the contagion of cholera, he has palpitations on mounting a step-ladder, finds it unpleasant to ride on the top of a coach or to look out of even a first-story window, and has never used an elevator. [abstract of Verga's report in American Journal of Psychology, November 1888]
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contract (v.)

late 14c., "to draw into a smaller compass, become smaller, shrink" (intransitive); early 15c. "make an agreement, enter into a contract, agree or establish to undertake mutually," from Old French contracter and directly from Latin contractus, past participle of contrahere "to draw several objects together; draw in, shorten, lessen, abridge," metaphorically "make a bargain, make an agreement," from assimilated form of com "with, together" (see con-) + trahere "to draw" (see tract (n.1)). Related: Contracted; contracting.

Meaning "to acquire as by habit or contagion, become infected with" is from 1590s. Transitive sense of "make narrow, draw together the parts (of something) to cause it to shrink" is from c. 1600. Grammatical sense of "to shorten (a word or syllable) by combining or eliding concurrent elements" is from c. 1600. Transitive sense of "arrange for by contract" is from 1897.

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