noun

virus

/ˈvaɪrəs/ · say it: VY·rəs

a tiny infectious agent that replicates inside host cells

In Science & Nature

In more detail

1. (noun) a tiny living thing that causes infectious diseases in humans, animals, and plants

2. (noun) a harmful computer program that spreads from one computer to another and damages files or data

Examples

1. She caught a virus and had to stay home from work.
2. The computer virus deleted all my documents.

How to use virus

Virus is used both in medical contexts to describe infectious agents causing disease and in computing to describe malicious software. In everyday English, it often refers colloquially to any minor illness (though technically incorrect for non-viral infections). The term is neutral in register and commonly used in both scientific and informal speech.

Common phrases

spread a virus
catch a virus
computer virus
viral infection
virus outbreak
antivirus software

Synonyms

pathogen · infection · bug · malware

Word family

viral (adjective) · virally (adverb)

A common mistake

Learners sometimes use 'virus' to refer to all infectious illnesses when technically only some diseases are viral (others are bacterial, fungal, etc.); also, confusing 'virus' with 'worm' or 'trojan' in computing contexts, though these are distinct types of malware.

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