side effect
Americannoun
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any effect of a drug, chemical, or other medicine that is in addition to its intended effect, especially an effect that is harmful or unpleasant.
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any accompanying or consequential and usually detrimental effect.
the side effects of air pollution.
noun
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any unwanted nontherapeutic effect caused by a drug Compare aftereffect
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any secondary effect, esp an undesirable one
Other Word Forms
Noun Inflected Forms
Etymology
Origin of side effect
First recorded in 1880–85
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Researchers have uncovered a surprising side effect of artificial lighting: ordinary streetlights can lure thousands of tiny land dwelling isopods into giant synchronized "death spirals."
From Science Daily ● Jul. 6, 2026
A side effect of that is a lack of empathy and curiosity.
From Los Angeles Times ● Jul. 1, 2026
The proposed rule, which would lower capital requirements for many banks, would likely have the side effect of lowering mortgage rates for many Americans.
From Barron's ● Jun. 29, 2026
But even people who don’t mean to hurt capybaras can still do harm to them, an unfortunate side effect of them living in such proximity to humans.
From Slate ● May 27, 2026
“It’s okay. I think it’s a side effect from... you know, your time in the Underworld. Hopefully it’ll get easier.”
From "The Son of Neptune" by Rick Riordan
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
