1. Of, exhibiting, or caused by radioactivity.
2. Informal. Extremely sensitive or controversial: "Perhaps race is now too radioactive a topic, in an era of political correctness" (David Nyhan).

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.