Definition of onium
: being or characterized by a usually complex cation
Origin of onium
First Known Use: 1905
Definition of -onium
: an ion having a positive charge <hydronium> — compare -ium 1b
Origin of -onium
New Latin, from ammonium
Medical Definition of onium
: being or characterized by a usually complex cation <onium salts>
Learn More about onium
Medical Dictionary: Definition of "onium"
Seen and Heard
What made you want to look up onium? Please tell us where you read or heard it (including the quote, if possible).