prot·​ac·​tin·​i·​um ˌprō-ˌtak-ˈti-nē-əm How to pronounce protactinium (audio)
: a shiny radioactive metallic element of relatively short life see Chemical Elements Table

Example Sentences

Recent Examples on the Web These natural uranium isotopes decay into the element thorium, which in turn decays into protactinium, and each has its own isotopes. Artemis Spyrou, The Conversation, 24 May 2022

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'protactinium.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Word History


New Latin

First Known Use

1918, in the meaning defined above

Time Traveler
The first known use of protactinium was in 1918

Dictionary Entries Near protactinium

Cite this Entry

“Protactinium.” Dictionary, Merriam-Webster, Accessed 1 Feb. 2023.

Kids Definition


prot·​ac·​tin·​i·​um ˌprōt-ˌak-ˈtin-ē-əm How to pronounce protactinium (audio)
: a shiny metallic radioactive element of short life see element

Medical Definition


prot·​ac·​tin·​i·​um ˌprōt-ˌak-ˈtin-ē-əm How to pronounce protactinium (audio)
variants also protoactinium
: a shiny metallic radioelement of relatively short life
symbol Pa
see Chemical Elements Table

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