vi·rus (v??r?s)n. pl. vi·rus·es 1. a. Any of various submicroscopic agents that infect living organisms, often causing disease, and that consist of a single or double strand of RNA or DNA surrounded by a protein coat. Unable to replicate without a host cell, viruses are typically not considered living organisms.b. A disease caused by a virus.2. A computer program or series of commands that can replicate itself and that spreads by inserting copies of itself into other files or programs which users later transfer to other computers. Viruses usually have a harmful effect, as in erasing all the data on a disk.3. A harmful or destructive influence: the pernicious virus of racism.[Latin v?rus, poison.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.virus (?va?r?s) n, pl -ruses1. (Microbiology) 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 pathogenic2. (Pathology) informal a disease caused by a virus3. any corrupting or infecting influence4. (Computer Science) 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 w?se marsh, Greek ios poison] ?virus-?like adjCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014vi?rus (?va? r?s) n., pl. -rus?es. 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. a disease caused by a virus. 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. [1590?1600;