/ Dictionary / Index P planetarium: Meaning and Definition of Find definitions for: plan•e•tar•i•um Pronunciation: (plan"i-târ'ē-um), [key] — pl. -tar•i•ums, -tar•i•a an apparatus or model representing the planetary system. a device that produces a representation of the heavens by the use of a number of moving projectors. the building or room in which such a device is housed. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: planetarium (Thesaurus) plane table planetary Related Content Daily Word Quiz: immense Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language