-ariumsuff. A place or device containing or associated with: planetarium.[Latin, neuter of -?rius, -ary.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.-arium suffix forming nouns indicating a place for or associated with something: aquarium; planetarium; solarium. [from Latin -?rium, neuter of -?rius -ary]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014-arium a suffix occurring in nouns denoting an artificial environment for plants or animals, on the model of vivarium or herbarium: aquarium; terrarium. Compare -ary. [