plural viruses
1
: an extremely small particle that causes a disease and that spreads from one person or animal to another
the AIDS virus = the virus that causes AIDS
Is the illness caused by bacteria or a virus?
2
: a disease or illness caused by a virus : a viral disease
I think I have the virus that's going around this winter.
a stomach virus
3
computers
: a program that is designed to harm a computer by deleting data, ruining files, etc., and that can be spread secretly from one computer to another
The software checks your hard drive for viruses.
Cite this Entry
“Virus.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/virus. Accessed 20 Jun. 2026.
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