[ahy-oh-nee-uh m]

noun Chemistry.

a naturally occurring radioactive isotope of thorium. Symbol: Io; atomic number: 90; atomic weight: 230.

Origin of ionium

First recorded in 1905–10; ion + -ium Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for ionium

Historical Examples of ionium

  • Ionium expels an alpha particle and becomes radium, which is a bivalent element resembling barium belonging to the second group.

    A Brief Account of Radio-activity

    Francis Preston Venable

British Dictionary definitions for ionium



obsolete a naturally occurring radioisotope of thorium with a mass number of 230Symbol: Io

Word Origin for ionium

C20: from New Latin, from ion + -ium
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012