onium

1 of 2

adjective

oni·um ˈō-nē-əm

: being or characterized by a usually complex cation

-onium

2 of 2

noun suffix

: an ion having a positive charge

hydronium

compare -ium sense 1b

Word History

Etymology

Adjective

-onium

Noun suffix

New Latin, from ammonium

First Known Use

Adjective

1905, in the meaning defined above

Time Traveler

The first known use of onium was in 1905

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-onium

onium

onkos

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Style

“Onium.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/onium. Accessed 30 Oct. 2025.

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Medical Definition

onium

adjective

oni·um ˈō-nē-əm

: being or characterized by a usually complex cation

onium salts

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onium

adjective

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