side effect

Or side-ef·fect

noun

1. 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.

2. any accompanying or consequential and usually detrimental effect.

   the side effects of air pollution.

side effect

noun

1. any unwanted nontherapeutic effect caused by a drug Compare aftereffect

2. any secondary effect, esp an undesirable one

Word History and Origins

Origin of side effect¹

First recorded in 1880–85

Related Words

• aftereffect 
• reaction