Word of the Day


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Liz Potter
Written by Liz Potter


negative, unpleasant or harmful

likely to cause problems

View the full definition in the Macmillan Dictionary

Origin and usage

The adjective adverse comes from the Latin ‘adversus’ meaning, among other things, unfavourable or harmful. It was first used in English in the 14th century.


The adjective adverse has been in the headlines following news that a trial of a promising Covid-19 vaccine has been temporarily halted due to an adverse reaction in one of the participants. Like many adjectives, adverse has a set of very strong noun collocates that fall into neat groups; you can explore them in the new Macmillan Collocations Dictionary here. Adverse is often used in medical contexts, particularly in relation to the effects of medication; collocates include ‘reaction’, ‘event’, ‘outcome’ and ‘effect’. Adverse is easily confused with ‘averse‘, which is almost always used in the structure ‘(not) be averse to something’. ‘Averse’ is never used before a noun except in the combination ‘risk-averse’, while adverse is almost always used before a noun; you don’t say the effects were adverse.


“The drug completed a Phase I clinical trial  without significant adverse events.”
(enTenTen15 corpus)

There have been no confirmed reports of adverse reactions due to consumption of these products.
(enTenTen15 corpus)

Additional crews may be added in times of adverse weather and high call volume.
(enTenTen15 corpus)

Related words

damaging, dangerous, harmful, risky

Browse related words in the Macmillan Thesaurus.

About the author

Liz Potter

Liz Potter

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