isotope

noun

iso·​tope ˈī-sə-ˌtōp How to pronounce isotope (audio)
1
: any of two or more species of atoms of a chemical element with the same atomic number and nearly identical chemical behavior but with differing atomic mass or mass number and different physical properties
2
: nuclide
isotopic
ˌī-sə-ˈtä-pik How to pronounce isotope (audio) -ˈtō- How to pronounce isotope (audio)
adjective
isotopically
ˌī-sə-ˈtä-pi-k(ə-)lē How to pronounce isotope (audio) -ˈtō- How to pronounce isotope (audio)
adverb

Examples of isotope 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.
Line Islands corals show a similar mean increase but far wider scatter, which the researchers partly attribute to these records’ reliance on oxygen isotopes alone. — Jacek Krywko, ArsTechnica, 31 Aug. 2026 The company was founded by entrepreneurs and isotope-enrichment specialists from Los Alamos National Laboratory. — Neetika Walter, Interesting Engineering, 31 Aug. 2026 By analyzing the tooth enamel, the stable isotope experts concluded that the soldiers’ diets were consistent with a European diet of wheat, barley and oats. — Jennifer Janofsky, The Conversation, 28 Aug. 2026 Likewise, the ratio of two different isotopes of oxygen in the coral changes with the water temperature. — Andrea Thompson, Scientific American, 27 Aug. 2026 See All Example Sentences for isotope

Word History

Etymology

is- + Greek topos place

First Known Use

1913, in the meaning defined at sense 1

Time Traveler
The first known use of isotope was in 1913

Rhymes for isotope

See All Rhymes for isotope

Browse Nearby Words

isotonize
isotope
isotope effect
See all Nearby Words

Cite this Entry

“Isotope.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/isotope. Accessed 3 Sep. 2026.

Copy Citation

Kids Definition

isotope

noun
iso·​tope ˈī-sə-ˌtōp How to pronounce isotope (audio)
: any of the forms of an element that differ in the number of neutrons in an atom
isotopic
ˌī-sə-ˈtäp-ik How to pronounce isotope (audio)
-ˈtō-pik
adjective
isotopically
-ˈtäp-i-k(ə-)lē How to pronounce isotope (audio)
-ˈtō-pi-
adverb

Medical Definition

isotope

noun
iso·​tope ˈī-sə-ˌtōp How to pronounce isotope (audio)
1
: any of two or more species of atoms of a chemical element with the same atomic number and position in the periodic table and nearly identical chemical behavior but with differing atomic mass or mass number and different physical properties
2
: nuclide
isotopic
ˌī-sə-ˈtäp-ik How to pronounce isotope (audio) -ˈtō-pik How to pronounce isotope (audio)
adjective
isotopically
-ˈtäp-i-k(ə-)lē How to pronounce isotope (audio) -ˈtō-pi- How to pronounce isotope (audio)
adverb
isotopy
ˈī-sə-ˌtō-pē How to pronounce isotope (audio) ī-ˈsät-ə-pē How to pronounce isotope (audio)
noun
plural isotopies

More from Merriam-Webster on isotope

Britannica.com: Encyclopedia article about isotope

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

A Who’s Who Regarding ‘Who’s’ and ‘Whose’

A List of Most Commonly Confused Words

Why do we use apostrophes to show possession?

Is it 'nerve-racking' or 'nerve-wracking'?

What's the difference between 'fascism' and 'socialism'?
See More

Popular in Wordplay

See More

The Longest Long Words List

Stay Woke

Ye Olde Nincompoop: Old-Fashioned Words for 'Stupid'

14 Phobias You Probably Haven't Heard Of

Even More Bird Names that Sound Like Insults (and Sometimes Are)
See More

Popular

See More

A Who’s Who Regarding ‘Who’s’ and ‘Whose’

The Longest Long Words List

Stay Woke
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
skateboard-dog-hat
Wordmaxxing Slang Quiz Give your vocabulary a glow up by getting sendy w...
See All