thorium

actinium$\longleftarrow$ 90 $\longrightarrow$protactinium

Pronunciation

• enPR: thôr'ēəm, IPA ^(key): /ˈθɔːriəm/

• Audio (US)

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Noun

Singular thorium

Plural none

1. (uncountable) Thorium is a radioactive element with an atomic number of 90 and symbol Th.