negative, unpleasant or harmful
likely to cause problems
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.”
“There have been no confirmed reports of adverse reactions due to consumption of these products.”
“Additional crews may be added in times of adverse weather and high call volume.”
damaging, dangerous, harmful, risky