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.
Tritium is a rare radioactive isotope of hydrogen used to fuel fusion reactions. — Aman Tripathi, Interesting Engineering, 7 Oct. 2026 Inserting neutrons into the uranium mix forces some of them to transform into a more reactive material, such as the isotope plutonium-239. — Mike McRae 06, New Atlas, 6 Oct. 2026 These systems convert heat from the natural radioactive decay of isotopes into electricity. — Selam Gebrekidan, New York Times, 4 Oct. 2026 Drug developers also use accelerators to produce radiopharmaceuticals, which are drugs that contain a radioactive isotope. — Andrea Richard, The Conversation, 2 Oct. 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 14 Oct. 2026.

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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

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