planetarium

noun

plan·​e·​tar·​i·​um ˌpla-nə-ˈter-ē-əm 

plural planetariums or planetaria ˌpla-nə-ˈter-ē-ə 

1

: a model or representation of the solar system

2

a

: an optical device for projecting various celestial images and effects

b

: a building or room housing such a projector

Examples of planetarium in a Sentence

Recent Examples on the Web

The resort has fantastic non-skiing activities, including a planetarium and observatory that guests can visit, and a mountain coaster. —Lydia Mansel, Travel + Leisure, 5 Jan. 2026

Or Frost Science in Miami turns everyone into a kid — sharks circling a multi-story aquarium, planetarium shows that reset anyone’s sense of scale, exhibits that invite visitors to touch first and read second. —Eric Barton, Sun Sentinel, 4 Jan. 2026

In that case, a 37-year-old convict with more than a year left to serve for theft fled during an outing to a planetarium. —Christina Coulter, PEOPLE, 28 Nov. 2025

Oahu’s Bishop Museum has a planetarium specifically set up to teach celestial navigation. —Literary Hub, 21 Oct. 2025

Word History

First Known Use

1860, in the meaning defined at sense 1

Rhymes for planetarium

• honorarium
• sanitarium
• aquarium
• herbarium
• ovarium
• puparium
• samarium
• zoarium
• armamentarium
• cerium

Kids Definition

planetarium

noun

plan·​e·​tar·​i·​um ˌplan-ə-ˈter-ē-əm 

plural planetariums or planetaria -ē-ə 

1

: a device that projects images of heavenly bodies on a ceiling shaped like a dome

2

: a building or room housing a planetarium