Etymology
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infectious (adj.)

"catching, having the quality of spreading from person to person, communicable by infection," 1540s of diseases, 1610s of emotions, actions, etc.; see infection + -ous. Earlier in the same sense were infectuous (late 15c.), infective (late 14c.). Related: Infectiously; infectiousness.

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catching (adj.)

1580s, of diseases, "communicating, infectious," present-participle adjective from catch (v.). From 1650s as "captivating." Related: Catchingly.

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infective (adj.)

"infectious, communicable by infection," late 14c., from Latin infectivus, from infect-, past participle stem of inficere "to tinge, dye; stain, spoil" (see infect).

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disinfectant (n.)

"agent used for destroying the germs of infectious diseases," 1837, from French désinfectant (1816), noun use of present participle of désinfecter (see disinfect), or else from the adjective in English (by 1827), "serving to disinfect." Related: Disinfection.

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pestilential (adj.)

late 14c., pestilencial, "producing or tending to produce an infectious disease, characterized by the plague," from Medieval Latin pestilentialis, from Latin pestilentia "plague" (see pestilence). Weakened sense of "mischievous, pernicious" is from 1530s. Related: Pestilentially.

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tetanus (n.)

infectious disease, late 14c., from Latin tetanus "tetanus," from Greek tetanos "tetanus, muscular spasm," literally "a stretching, tension," from teinein "to stretch" (from PIE root *ten- "to stretch"); "so called because the disease is characterized by violent spasms and stiffness of the muscles" [Barnhart]. Related: Tetanoid (adj.).

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rabies (n.)

"extremely fatal infectious disease of dogs, humans, and many other mammals," 1590s, from Latin rabies "madness, rage, fury," related to rabere "be mad, rave" (see rage (v.)). The mad-dog disease sense was a secondary meaning of the Latin noun. Known as hydrophobia (q.v.) in humans. Related: Rabietic.

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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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pest (n.)

1550s (in imprecations, "a pest upon ____," etc.), "plague, pestilence, epidemic disease," from French peste (1530s), from Latin pestis "deadly contagious disease; a curse, bane," a word of uncertain origin. Meaning "any noxious, destructive, or troublesome person or thing" is attested by c. 1600. Pest-house "hospital for persons suffering from infectious diseases" is from 1610s.

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pestilence (n.)

c. 1300, "any infectious or contagious disease, fatal epidemic," from Old French pestilence "plague, epidemic" (12c.) and directly from Latin pestilentia "a plague, an unwholesome atmosphere," noun of condition from pestilentem (nominative pestilens) "infected, unwholesome, noxious," from pestis "deadly disease, plague" (see pest).

Also in Middle English "wickedness, evil, sin, a vice, that which is morally pestilential."

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