The American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
noun pl. at·mo·spher·i·a
An optical device designed to project images of atmospheric phenomena, such as clouds, on the inside of a dome.
Origin: atmospher(e) + (planetar)ium.