definitions

side effect

or side-ef·fect

SEE MORE SYNONYMS FOR side effect ON THESAURUS.COM

noun

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.
any accompanying or consequential and usually detrimental effect: the side effects of air pollution.

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RELATED WORDS

reaction, aftereffect, aftermath, concomitant, corollary, leftover, offshoot, spinoff, aftertaste, byproduct, sidebar

Nearby words

side circuit, side curl, side deal, side dish, side drum, side effect, side horse, side meat, side money, side of the tracks, side pot

Origin of side effect

First recorded in 1880–85
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for side effect

side effect

noun

any unwanted nontherapeutic effect caused by a drugCompare aftereffect (def. 2)
any secondary effect, esp an undesirable one
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Medicine definitions for side effect

side effect

n.

A peripheral or secondary effect, especially an undesirable secondary effect of a drug or therapeutic regimen.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.