Reactive means dealing with things once they happen instead of getting ahead of them. A council that fixes potholes only after the complaints arrive is being reactive, and so is the manager who does nothing until an email turns up in capital letters.
In that sense the word is a criticism, and it lives in the shadow of its opposite, proactive, the pair turning up in every job advert and staff appraisal. Chemistry uses reactive with no judgement in it at all, where a reactive element takes part in reactions readily, which is why sodium is kept under oil and gold is not. Medicine borrows it for a test that shows a response and for a condition that arises as a response to something else. The noun is reactivity and the verb behind them all is react. Keep it apart from reactionary, which is political and means wanting to turn the clock back.
1adjectivereactiveResponding to events after they happen rather than planning ahead.~8%
“Their security work is entirely reactive; nobody looks for problems in advance.”
2adjectivechemistryIn chemistry, quick to take part in chemical reactions.~31%
“Fluorine is the most reactive element in its group.”
3adjectiveresponseHappening as a response to something else, or showing a response in a test.~61%
“The swelling was reactive and cleared once the infection was treated.”
Shares are an estimate: a language model read 13 sentences found in the wild and placed 13 of them on a sense — a count of our sample, not a measurement of English.
From react + -ive.
Etymology from Wiktionary, CC BY-SA