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.
This metric measures the effort needed to separate fissile uranium-235 from non-fissile isotopes. — Aman Tripathi, Interesting Engineering, 12 Aug. 2026 Next up will be looking at the meteorite's isotopes to figure out its connection to other meteorites formed early in Martian history. — Elizabeth Howell, Space.com, 11 Aug. 2026 Radiopharmaceuticals are an emerging type of treatment designed to shoot radioactive isotopes directly at tumor cells. — Allison Deangelis, STAT, 10 Aug. 2026 Park’s team then worked through the 450 years of mud bracketing that sliver, layer by layer, combining microscope images with chemical scans, isotope readings, and diatom counts every two to three years. — Jacek Krywko, ArsTechnica, 9 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 16 Aug. 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

Nglish: Translation of isotope for Spanish Speakers

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!

More from Merriam-Webster

Word of the Day

Listen to the pronunciation of zeugma

See Definitions and Examples »

Popular in Grammar & Usage

See More

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

7 Pairs of Commonly Confused Words

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?
See More

Popular in Wordplay

See More

Words from the 'Odyssey'

The Longest Long Words List

It's a Scorcher! Words for the Summer Heat

The Words of the Week - Aug. 14

12 Lovely and Unusual Words for the Natural World
See More

Popular

See More

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

Words from the 'Odyssey'

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
image of a green cube out of place in a lineup of red spheres
Odd Word Out: Synonyms Vol. 2 Quiz Figure out which word isn't like the others.
See All