adverse

adjective

Synonyms of adverse
1
: acting against or in a contrary direction : hostile
hindered by adverse winds
2
a
: opposed to one's interests
an adverse verdict
heard testimony adverse to their position
especially : unfavorable
adverse criticism
b
: causing harm : harmful
adverse drug effects
3
archaic : opposite in position
adverseness noun

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Adverse vs. Averse

Many people find themselves confused when faced with the choice between adverse and averse. While these two adjectives have many similarities, they are not used interchangeably.

If you want to describe a negative reaction to something (such as a harmful side effect from medication) or dangerous meteorological conditions (such as a snowstorm), adverse is the correct choice; you would not say that you had an averse reaction to medication or that there was averse weather.

Averse is most commonly followed by the preposition to (as in "she is averse to shellfish"), but not in every case; you can, for example, describe someone as “risk averse." Normally, averse to signifies a degree of dislike and avoidance, but when preceded by the word not (as in “he was not averse to having another drink”), it may be used as a pointedly understated way to express an interest in something.

In short, adverse tends to be used to describe effects, conditions, and results; while averse refers to feelings and inclinations.

Examples of adverse in a Sentence

The Bankruptcy Code requires that debtor's counsel be disinterested and not have an interest adverse to the estate. —Lawyers Weekly USA, 4 Oct. 1999
On more than one occasion his decrees provoked riots, and there were those who voiced adverse opinions on the Duke in public. —Alison Weir, The Princes in the Tower, 1992
The plant tolerates adverse conditions … —Dave Dunn, Fine Gardening, January/February 1991
all the adverse publicity really caused the movie star's popularity to suffer the adverse effects of the drug are too severe to allow it to be marketed
Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
But the fact that Ammann’s platelet count, like Lanitis’s and Hawrylak’s, had been impacted after the alpha-lipoic- acid infusion suggested that Ammann, too, might have had an adverse response. — D. T. Max, New Yorker, 26 Oct. 2026 In recent years, cocoa prices have surged due to adverse weather across key West African producing regions. — CNBC, 23 Oct. 2026 The researchers did not assess parenting quality or childrenâs health, and the findings do not establish that parental cannabis use causes adverse child outcomes. — Melissa Rudy, FOXNews.com, 22 Oct. 2026 Lutikizumab was generally safe and well tolerated, with adverse event rates that were nearly identical between the placebo and treatment groups. — Jonathan Wosen, STAT, 22 Oct. 2026 See All Example Sentences for adverse

Word History

Etymology

Middle English, borrowed from Anglo-French advers, borrowed from Latin adversus "turned toward, facing, opposed," from past participle of advertere "to turn toward, direct" — more at advert entry 1

First Known Use

14th century, in the meaning defined at sense 1

Time Traveler
The first known use of adverse was in the 14th century

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Cite this Entry

“Adverse.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/adverse. Accessed 27 Oct. 2026.

Kids Definition

adverse

adjective
1
: acting in an opposite direction
adverse winds
2
: opposed to one's interests
adverse testimony
especially : not friendly or favorable
adverse criticism
3
: causing harm
adverse effects of a drug
adversely adverb
adverseness noun

Legal Definition

: opposed to one's interests : operating to one's detriment
an adverse verdict
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