n., pl., -i·ums, or -i·a (-ē-ə).
- An apparatus or model representing the solar system.
- An optical device for projecting images of celestial bodies and other astronomical phenomena onto the inner surface of a hemispherical dome.
- A building or room containing a planetarium, with seats for an audience.
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.
