Viruses

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.
noun (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

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

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.

A disease caused by a virus.

virus
(vī’rəs)
Plural viruses

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.

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
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.

virus