reacts; reacted; reacting
1
: to behave or change in a particular way when something happens, is said, etc.
When I told her what happened, she reacted with anger.
I didn't expect him to react that way.
The firefighters reacted quickly when they heard the alarm.
—often + toShe reacted to the news by getting angry.
Most people reacted positively to the smoking ban.
2
of a chemical substance
: to change after coming into contact with another substance
—often + with
The chemicals react with each other to form a gas.
—often + togetherOzone is formed in the atmosphere when sunlight and hydrocarbons react together.
3
medical
: to be affected by a drug, food, etc., in usually a bad way
He reacted badly to the drug.
Cite this Entry
“React.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/react. Accessed 22 Jun. 2026.
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