isomer

noun

iso·​mer ˈī-sə-mər 

1

: one of two or more compounds, radicals, or ions that contain the same number of atoms of the same elements but differ in structural arrangement and properties

2

: a nuclide isomeric with one or more others

Examples of isomer in a Sentence

Recent Examples on the Web

However, heat processing during canning altered the lutein and zeaxanthin isomers, which are structural variants considered less biologically active as antioxidants than their naturally occurring forms. — Anna Giorgi, Verywell Health, 2 July 2026

But the Dewar isomers of the pyrimidones are incredibly stable. — Jacek Krywko, ArsTechnica, 16 Feb. 2026

That is the more potent of the drug’s two isomers and can be found in both street meth and prescription medications such as Desoxyn. — Daniel Libit, Sportico.com, 21 Jan. 2026

Should Trump pursue this scheme of conquest, the military’s training will have to be shattered and reassembled into a destructive version of itself, as if doctors were asked to take lifesaving medicines, reconstitute them as poisonous isomers, and then administer them to patients. — Tom Nichols, The Atlantic, 19 Jan. 2026

Word History

Etymology

International Scientific Vocabulary, back-formation from isomeric

First Known Use

1855, in the meaning defined at sense 1

Phrases Containing isomer

• structural isomer

Kids Definition

isomer

noun

iso·​mer ˈī-sə-mər 

: one of two or more chemical compounds or groups that have the same numbers of atoms of the same elements but differ in structure

isomeric

ˌī-sə-ˈmer-ik

adjective

isomerism

ī-ˈsäm-ə-ˌriz-əm

noun

Medical Definition

isomer

noun

iso·​mer ˈī-sə-mər 

1

: any of two or more compounds, radicals, or ions that contain the same number of atoms of the same elements but differ in structural arrangement and properties

2

: a nuclide isomeric with one or more others