Etymology
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echovirus (n.)
also ECHO virus, 1955, acronym for enteric cytopathogenic human orphan; "orphan" because when discovered they were not known to cause any disease.
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inoculation (n.)

mid-15c. in horticulture, "act or practice of grafting buds;" 1714 in pathology, "insertion of a form of a virus in order to prevent a more serious attack of it," from Latin inoculationem (nominative inoculatio) "an engrafting, budding," noun of action from past-participle stem of inoculare (see inoculate).

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coronavirus (n.)

type of RNA virus affecting birds and mammals, in humans as a respiratory tract infection, by 1968, is so called for the spikes that protrude from its membranes and resemble the corona of the sun; see corona.  Covid as a contraction of coronavirus disease seems to have been coined for the outbreak that began in China in 2019 (COVID-19).

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acerbity (n.)
Origin and meaning of acerbity

1570s, from French acerbité, from Latin acerbitatem (nominative acerbitas) "harshness, sharpness, bitterness, sourness," literal and figurative (as in virus acerbitatis "the poison of malice"), from acerbus "bitter to taste, sharp, sour, tart," from Proto-Italic *akro-po- "sharp" (from PIE root *ak- "be sharp, rise (out) to a point, pierce"). Earliest use in English is figurative, of "sharp and bitter" persons. Of tastes, from 1610s. Latin acerbus is related to acer "sharp" as superbus "haughty" to super "above."

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influenza (n.)

type of infectious disease, now known to be caused by a virus, usually occurring as an epidemic, with symptoms similar to a severe cold along with high fever and rapid prostration, 1743, borrowed (during an outbreak of the disease in Europe), from Italian influenza "influenza, epidemic," originally "visitation, influence (of the stars)," from Medieval Latin influentia in the astrological sense (see influence).

AN Article from Rome informs us that a Sort of Plague has broke out there, which destroys Abundance of their People, and they call it the Influenza. [The Gentleman's Magazine, April 1743]

Used in Italian for diseases at least since 1504 (as in influenza di febbre scarlattina "scarlet fever") on notion of astral, occult, or atmospheric influence. The 1743 outbreak began in Italy. Often applied since mid-19c. to severe colds.

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Trojan (adj.)
Old English Troian "of or pertaining to ancient Troy," from Latin Trojanus, from Troia, Troja "Troy," from the Greek name for the city, said to be from Tros, name of a king of Phrygia, the mythical founder of Troy. Trojan horse was figurative of ambush-from-within in Roman times (equus Troianus); attested in English from 1570s; the computer virus sense is attested by 1982.

As a noun from mid-14c., "inhabitant of ancient Troy;" in early modern English, the noun could mean "a determined fellow, one who fights or works hard," from the Trojans' long resistance to the Greeks in the Trojan War, but also in 17c., it was a colloquial term for "person of dissolute life, carousing companion." The trade name for a brand of prophylactic contraceptive was registered 1927 in U.S.
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vaccination (n.)

1800, used by British physician Edward Jenner (1749-1823) for the technique he publicized of preventing smallpox by injecting people with the similar but much milder cowpox virus (variolae vaccinae), from vaccine (adj.) "pertaining to cows, from cows" (1798), from Latin vaccinus "from cows," from vacca "cow," a word of uncertain origin. A mild case of cowpox rendered one immune thereafter to smallpox. "The use of the term for diseases other than smallpox is due to Pasteur" [OED].

The earlier 18c. method of smallpox protection in England was by a kind of inoculation called  variolation (from variola, the medical Latin word for "smallpox"). There are two forms of smallpox: a minor one that killed 2% or less of the people who got it, and a virulent form that had about a 30% mortality rate and typically left survivors with severe scarring and often blinded them. Those who got the minor form were noted to be immune thereafter to the worse. Doctors would deliberately infect healthy young patients with a local dose of the minor smallpox, usually resulting in a mild case of it at worst, to render them immune to the more deadly form. Jenner's method was safer, as it involved no smallpox exposure.

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