hydronium

noun

hy·​dro·​ni·​um hī-ˈdrō-nē-əm How to pronounce hydronium (audio)
: a hydrated hydrogen ion H3O+

Examples of hydronium in a Sentence

Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
The movement of each electron is timed and arranged just so to cause a proton in the form of a hydronium ion, which is positively charged, to head in the opposite direction. — James Somers, The New Yorker, 25 Oct. 2022 Laboratory work has shown that ice naturally contains ionic defects—hydronium (H₃O⁺) and hydroxide (OH⁻) ions. — Tejasri Gururaj, Interesting Engineering, 30 Dec. 2025

Word History

Etymology

International Scientific Vocabulary hydr- + -onium

First Known Use

1908, in the meaning defined above

Time Traveler
The first known use of hydronium was in 1908

Rhymes for hydronium

See All Rhymes for hydronium

Browse Nearby Words

hydronitrogen
hydronium
hydronymy
See all Nearby Words

Cite this Entry

“Hydronium.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/hydronium. Accessed 7 Jul. 2026.

Copy Citation

Kids Definition

hydronium

noun
hy·​dro·​ni·​um hī-ˈdrō-nē-əm How to pronounce hydronium (audio)
: an ion formed by the combination of a hydrogen ion with a water molecule

Medical Definition

hydronium

noun
hy·​dro·​ni·​um hī-ˈdrō-nē-əm How to pronounce hydronium (audio)
: a hydrated hydrogen ion H3O+
Last Updated: - Updated example sentences
Love words? Need even more definitions?

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

Popular in Grammar & Usage

See More

Is that lie 'bald-faced' or 'bold-faced'?

'A' or 'an'? What about before 'h'? An Indefinite Article Guide

Why is '-ed' sometimes pronounced at the end of a word?

Commonly Misspelled Words

How to Use Em Dashes (—), En Dashes (–) , and Hyphens (-)
See More

Popular in Wordplay

See More

14 Phobias You Probably Haven't Heard Of

The Longest Long Words List

One-Word Oxymorons: Bittersweet, Spendthrift, and More

Ten Words Ending with a Silent ‘T’

12 Lovely and Unusual Words for the Natural World
See More

Popular

See More

Is that lie 'bald-faced' or 'bold-faced'?

14 Phobias You Probably Haven't Heard Of

The Longest Long Words List
See More

Games & Quizzes

See All
Play Quordle: Guess all four words in a limited number of tries. Each of your guesses must be a real 5-letter word.
Quordle Can you solve 4 words at once?
Play Blossom: Solve today's spelling word game by finding as many words as you can using just 7 letters. Longer words score more points.
Blossom Pick the best words!
Play Missing Letter: a crossword with a twist. Each of the 25 puzzle words start with a different letter of the alphabet. Which letter is missing?
The Missing Letter A daily crossword with a twist
hangman letters and game
Hangman Lightning Round Figure out which word fits in the blanks.
See All