virus

[vahy-ruhs]
noun, plural viruses.
1.
an ultramicroscopic (20 to 300 nm in diameter), metabolically inert, infectious agent that replicates only within the cells of living hosts, mainly bacteria, plants, and animals: composed of an RNA or DNA core, a protein coat, and, in more complex types, a surrounding envelope.
2.
Informal. a viral disease.
3.
a corrupting influence on morals or the intellect; poison.
4.
a segment of self-replicating code planted illegally in a computer program, often to damage or shut down a system or network.

Origin:
1590–1600; < Latin vīrus slime, poison; akin to ooze2

viruslike, adjective
antivirus, adjective
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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Collins
World English Dictionary
virus (ˈvaɪrəs)
 
n , pl -ruses
1.  any of a group of submicroscopic entities consisting of a single nucleic acid chain surrounded by a protein coat and capable of replication only within the cells of living organisms: many are pathogenic
2.  informal a disease caused by a virus
3.  any corrupting or infecting influence
4.  computing an unauthorized program that inserts itself into a computer system and then propagates itself to other computers via networks or disks; when activated it interferes with the operation of the computer
 
[C16: from Latin: slime, poisonous liquid; related to Old English wāse marsh, Greek ios poison]
 
'virus-like
 
adj

Collins English Dictionary - Complete & Unabridged 10th Edition
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Etymonline
Word Origin & History

virus
1392, "venomous substance," from L. virus "poison, sap of plants, slimy liquid," probably from PIE base *weis- "to melt away, to flow," used of foul or malodorous fluids (cf. Skt. visam "poison," visah "poisonous;" Avestan vish- "poison;" L. viscum "sticky substance, birdlime;" Gk. ios "poison," ixos
"mistletoe, birdlime; O.C.S. vinja "cherry;" O.Ir. fi "poison;" Welsh gwy "fluid, water," gwyar "blood"). Main modern meaning "agent that causes infectious disease" first recorded 1728. The computer sense is from 1972. Adjective form viral was coined 1948.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

virus vi·rus (vī'rəs)
n. pl. vi·rus·es

  1. Any of various simple submicroscopic parasites of plants, animals, and bacteria that often cause disease and that consist essentially of a core of RNA or DNA surrounded by a protein coat. Unable to replicate without a host cell, viruses are typically not considered living organisms.

  2. A disease caused by a virus.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
virus   (vī'rəs)  Pronunciation Key 
Plural viruses
  1. Any of various extremely small, often disease-causing agents consisting of a particle (the virion), containing a segment of RNA or DNA within a protein coat known as a capsid. Viruses are not technically considered living organisms because they are devoid of biological processes (such as metabolism and respiration) and cannot reproduce on their own but require a living cell (of a plant, animal, or bacterium) to make more viruses. Viruses reproduce first either by injecting their genetic material into the host cell or by fully entering the cell and shedding their protein coat. The genetic material may then be incorporated into the cell's own genome or remain in the cytoplasm. Eventually the viral genes instruct the cell to produce new viruses, which often cause the cell to die upon their exit. Rather than being primordial forms of life, viruses probably evolved from rogue pieces of cellular nucleic acids. The common cold, influenza, chickenpox, smallpox, measles, mumps, yellow fever, hemorrhagic fevers, and some cancers are among the diseases caused by viruses.

  2. Computer Science A computer program that duplicates itself in a manner that is harmful to normal computer use. Most viruses work by attaching themselves to another program. The amount of damage varies; viruses may erase all data or do nothing but reproduce themselves.


viral adjective
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Cultural Dictionary
virus [(veye-ruhs)]

plur. viruses

Microorganisms consisting of DNA and RNA molecules wrapped in a protective coating of proteins. Viruses are the most primitive form of life. They depend on other living cells for their reproduction and growth. (See under “Medicine and Health.”)

Note: Viruses cause many diseases. (See viral infection.)
virus [(veye-ruhs)]

plur. viruses

A minute organism that consists of a core of nucleic acid surrounded by protein. Viruses, which are so small that a special kind of microscope is needed to view them, can grow and reproduce only inside living cells. (See under “Life Sciences.”)

virus definition


See computer virus.

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Slang Dictionary

virus

n. [from the obvious analogy with biological viruses, via SF] A cracker program that searches out other programs and `infects' them by embedding a copy of itself in them, so that they become Trojan horses. When these programs are executed, the embedded virus is executed too, thus propagating the `infection'. This normally happens invisibly to the user. Unlike a worm, a virus cannot infect other computers without assistance. It is propagated by vectors such as humans trading programs with their friends (see SEX). The virus may do nothing but propagate itself and then allow the program to run normally. Usually, however, after propagating silently for a while, it starts doing things like writing cute messages on the terminal or playing strange tricks with the display (some viruses include nice display hacks). Many nasty viruses, written by particularly perversely minded crackers, do irreversible damage, like nuking all the user's files.

In the 1990s, viruses have become a serious problem, especially among Wintel and Macintosh users; the lack of security on these machines enables viruses to spread easily, even infecting the operating system (Unix machines, by contrast, are immune to such attacks). The production of special anti-virus software has become an industry, and a number of exaggerated media reports have caused outbreaks of near hysteria among users; many lusers tend to blame _everything_ that doesn't work as they had expected on virus attacks. Accordingly, this sense of `virus' has passed not only into techspeak but into also popular usage (where it is often incorrectly used to denote a worm or even a Trojan horse). See phage; compare back door; see also Unix conspiracy.
FOLDOC
Computing Dictionary

virus definition

security
(By analogy with biological viruses, via science fiction) A program or piece of code, a type of malware, written by a cracker, that "infects" one or more other programs by embedding a copy of itself in them, so that they become Trojan horses. When these programs are executed, the embedded virus is executed too, thus propagating the "infection". This normally happens invisibly to the user.
A virus has an "engine" - code that enables it to propagate and optionally a "payload" - what it does apart from propagating. It needs a "host" - the particular hardware and software environment on which it can run and a "trigger" - the event that starts it running.
Unlike a worm, a virus cannot infect other computers without assistance. It is propagated by vectors such as humans trading programs with their friends (see SEX). The virus may do nothing but propagate itself and then allow the program to run normally. Usually, however, after propagating silently for a while, it starts doing things like writing "cute" messages on the terminal or playing strange tricks with the display (some viruses include display hacks). Viruses written by particularly antisocial crackers may do irreversible damage, like deleting files.
By the 1990s, viruses had become a serious problem, especially among IBM PC and Macintosh users (the lack of security on these machines enables viruses to spread easily, even infecting the operating system). The production of special antivirus software has become an industry, and a number of exaggerated media reports have caused outbreaks of near hysteria among users. Many lusers tend to blame *everything* that doesn't work as they had expected on virus attacks. Accordingly, this sense of "virus" has passed into popular usage where it is often incorrectly used for other types of malware such as worms or Trojan horses.
See boot virus, phage. Compare back door. See also Unix conspiracy.
[Jargon File]
(2003-06-20)
The Free On-line Dictionary of Computing, © Denis Howe 2010 http://foldoc.org
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Example sentences
The typical safety office will monitor biohazards produced from research on,
  say, a virulent virus or bacterium.
The influenza virus mutates so quickly that last year's vaccination is usually
  ineffective against this year's bug.
Rather than going after the virus itself, these compounds would inhibit
  molecules native to the patient.
In fact, almost half of all crew members that worked the plane over the next
  five days picked up the virus.
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