Tending to be responsive or to react to a stimulus.(adjective)
Characterized by reaction.(adjective)
Chemistry &amp; Physics Tending to participate readily in reactions.(adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "reactive" in a sentence
"The author then enters into a discussion of the use of the term reactive tendency, and explains that this term, according to his definition, is meant to explain something more specific than an inclination to direct activity toward one of a limited number of general ends, and to include both the innate and the acquired features of an individual's reactive mechanism."
"Georgia suffered from troubled breathing when she had a cold or a cough, and had been in the ER twice for what they call reactive airway disease -- or heavy wheezing due to constricted airways."
"In a posting on its website over the weekend, the hospital said the mistake occurred because a transplant staffer believed that the English word "reactive" on the donor's standard HIV test meant negative instead of positive."