To save this word, you'll need to log in.
oni·um | \ ˈō-nē-əm 
\
\Definition of onium
(Entry 1 of 2)
: being or characterized by a usually complex cation
-onium
noun suffixDefinition of -onium (Entry 2 of 2)
: an ion having a positive charge
hydronium — compare -ium sense 1b
Keep scrolling for more
Keep scrolling for more
More Definitions for onium
onium
adjectiveoni·um | \ ˈō-nē-əm \
\Medical Definition of onium
: being or characterized by a usually complex cation
onium salts
Comments on onium
What made you want to look up onium? Please tell us where you read or heard it (including the quote, if possible).
Test Your Vocabulary
Pass the Little Ribbons: A Pasta Word Quiz
- Match the pasta to its meaning in English: Rotelle
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
- Pass the Little Ribbons: A Pasta Word Quiz
Match the pasta with its meaning in Italian.
Take the quiz - Confusing Words—A Quiz
Test your knowledge of these commonly confused words!
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 onium
Resources for onium