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io·ni·um | \ ī-ˈō-nē-əm 
\
\Definition of ionium
: a natural radioactive isotope of thorium having a mass number of 230
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ionium
nounio·ni·um | \ ī-ˈō-nē-əm \
\Medical Definition of ionium
: a natural radioactive isotope of thorium having a mass number of 230
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Time Traveler for ionium
The first known use of ionium was in 1907
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