1. A steep, sharply curving elevated railway with small open passenger cars that is operated at high speeds as a ride, especially in an amusement park.
2. An action, event, or experience marked by abrupt, extreme changes in circumstance, quality, or behavior: "the demographic roller coaster caused by the baby boom" (American Demographics).

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.