To save this word, you'll need to log in.
ac·tin·i·um | \ ak-ˈti-nē-əm 
\
\Definition of actinium
: a radioactive trivalent metallic element that resembles lanthanum in chemical properties and that is found especially in pitchblende — see Chemical Elements Table
Keep scrolling for more
Keep scrolling for more
More Definitions for actinium
actinium
nounac·tin·i·um | \ ak-ˈtin-ē-əm \
\Medical Definition of actinium
: a radioactive trivalent metallic element that resembles lanthanum in chemical properties and that is found especially in pitchblende
—symbol Ac — see Chemical Elements Table
Comments on actinium
What made you want to look up actinium? Please tell us where you read or heard it (including the quote, if possible).
Test Your Vocabulary
More Confusing Words—Quiz
- The magician
______moved the selected card to the top of the deck.
Can you spell these 10 commonly misspelled words?
TAKE THE QUIZ
Test Your Knowledge - and learn some interesting things along the way.
TAKE THE QUIZLove words? Need even more definitions?
Merriam-Webster unabridgedWords at Play
Ask the Editors
Word Games
- More Confusing Words—Quiz
How many of these commonly confused words do you know?
Take the quiz - Name that Thing: Toys and Games Edition
It's all fun and games until someone beats your high score.
Take the quiz - Spell It
Can you spell these 10 commonly misspelled words?
Take the quiz - Citation
Do you know the person or title these quotes describe?
Play the game
Share actinium
Time Traveler for actinium
The first known use of actinium was in 1900
See more words from the same year