Merriam-Webster Logo
SINCE 1828
Menu
×

An Encyclopædia Britannica Company

See What's Trending Now See More Trending Words

ionium

play
noun io·ni·um \ī-ˈō-nē-əm\

Definition of ionium

  1. :  a natural radioactive isotope of thorium having a mass number of 230

Explore M-W

image1489982902
Devilish Words
watercolor-squares
We're Down With You Being—or Your Being?—a Square
alt-59973139034d4
Trending: 'Svengali' Bannon leaving White House
time-traveler-quiz-which-word-came-first
Time Traveler Quiz: Which Word Came First?

Origin and Etymology of ionium

ion; from its ionizing action

Medical Dictionary

ionium

play
noun io·ni·um \ī-ˈō-nē-əm\

Medical Definition of ionium

  1. :  a natural radioactive isotope of thorium having a mass number of 230

Learn More about ionium

  1. Britannica.com: Encyclopedia article about ionium

Seen and Heard

What made you want to look up ionium? Please tell us where you read or heard it (including the quote, if possible).

show hide

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

WORD OF THE DAY

depredate

play

to plunder or ravage

Get Word of the Day daily email!

TRENDING NOW

  1. Svengali 'A person who manipulates'

  2. syzygy An obscure astronomy term goes mainstream

  3. hegemon "Something having dominant influence over others"

  4. repugnant Trump clarifies his position on racism

  5. white nationalist, white supremacist Trending in 2017

SEE ALL

BROWSE DICTIONARY

ionium

Test Your Vocabulary

Time Traveler Quiz: Which Word Came First?

  • time-traveler-quiz-which-word-came-first
  • Which came first?
How Strong Is Your Vocabulary?

Test your vocabulary with our 10-question quiz!

TAKE THE QUIZ
Word Winder's CrossWinder

Test Your Knowledge - and learn some interesting things along the way.

TAKE THE QUIZ

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

Words at Play

watercolor-squares
We're Down With You Being—or Your Being?—a Square

It's about (you? your?) having your say.

image1489982902
Devilish Words

Don't blame a word use error on the devil.

alt-599492594f435
How 'Wonderful' Lost Its Sense of Wonder

A case of semantic bleaching

dog-covering-face
Don't Let Reading This Be Another 'Coulda' 'Shoulda' 'Woulda'

PSA: They're three separate words.

Ask the Editors

video-title-words-of-the-year-1066
Words of the Year: 1066

Or, Why Pig Meat is Called 'Pork' and Cow Meat is Called 'Beef'

payday
How Often Is 'Biweekly'?

Don't get us started on 'bimonthly'

video-irregardless-grammar-peeve-blend-of-the-synonyms-irrespective-and-regardless
Irregardless

It is in fact a real word (but that doesn't mean you should use it).

video-moose-goose-weird-plurals
Weird Plurals

One goose, two geese. One moose, two... moose. What's up with that?

Word Games

time-traveler-quiz-which-word-came-first
Time Traveler Quiz: Which Word Came First?

Which word entered the English language first?

Take the quiz
name-more-food
Name More Food!

Test your knowledge of food vocabulary!

Take the quiz
How Strong Is Your Vocabulary?
How Strong Is Your Vocabulary?

Test your vocabulary with our 10-question quiz!

Take the quiz
Word Winder's CrossWinder
Word Winder's CrossWinder

A game of winding words.

Play the game