tr.v. in·fect·ed, in·fect·ing, in·fects
1. To invade and proliferate in, often resulting in disease. Used of microorganisms or other infectious agents: people who were infected with salmonella.
2. To cause the invasion of (a cell, for example) with a microorganism or other infectious agent: The researchers infected the bacteria with a virus.
3. To transmit a pathogen or disease to: The sick child infected the entire class.
4. To contaminate with a pathogenic microorganism or agent: Cholera infected the water supply.
5. Computers To become transmitted to and copied on (a hard drive, for example). Used of a virus or other harmful software.
6. To affect by transmission or be communicated to. Used of an idea, emotion, or attitude: "His fear infected me, and ... I followed as fast as I could" (W.H. Hudson).
[Middle English infecten, to afflict with disease, from Latin īnficere, īnfect-, to stain, infect (in-, in; see IN-2 + facere, to do; see dhē- in the Appendix of Indo-European roots).]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.