isomer

/ˈaɪ.sə.mə/

//ˈaɪ.sə.mə// noun

By · According to Wiktionary data (CC BY-SA) ·

"isomer" is a 6-letter English headword indexed on PlainSpell.

The verdict

“isomer” is uncommon English (frequency #55,520 among 17,902 “I” headwords), classed as a noun. The kind of spelling people second-guess.

#55,520
frequency rank, English
17,902
“I” headwords

According to Wiktionary data (CC BY-SA, analyzed May 6, 2026) - Any of two or more compounds with the same molecular formula but with different structure.

Key facts for isomer
PropertyValue
Headwordisomer
LanguageEnglish
Part of speechNoun
IPA/ˈaɪ.sə.mə/
Letters6
Frequency rank#55,520
Misspellings tracked0
Confusable pairs0
SourceWiktionary (kaikki.org)

Where “isomer” sits in English frequency

Every-word frequency runs from the handful of words we use constantly (left) to the long tail used once in a blue moon (right). isomer lands here:

#1#100#1K#10K#100K
← used constantlyrarely used →

Scale is logarithmic (each tick is 10× rarer). Source: FrequencyWords open word-frequency list.

Rare enough to double-check

isomer is uncommon English at frequency #55,520 among 17,902 “I” headwords, classed as anoun, transcribed /ˈaɪ.sə.mə/. Rarity is why readers land here mid-draft. 2 senses are on record.

Zero misspellings are on record for isomer in our index, suggesting the orthography follows predictable English patterns. No close-neighbour confusable shows up for this headword in our dataset, suggesting its spelling stands apart enough that readers rarely confuse it with something else.

Etymologically, the entry records: From iso- + -mer. The correct English form is isomer, spelled I-S-O-M-E-R.

Definition

  1. 1
    Any of two or more compounds with the same molecular formula but with different structure.
  2. 2
    Any of two or more atomic nuclei with the same mass number and atomic number but with different radioactive properties.

Etymology

From iso- + -mer.

Synonyms

nuclear isomer

This word in other languages

isómero(Español)isomère(Français)Isomer(Deutsch)isômero(Português)

Definitions, pronunciation, and etymology for this entry are drawn from Wiktionary via the kaikki.org structured extract (CC BY-SA); frequency ordering uses the FrequencyWords open word-frequency list (2018 English corpus, MIT). See the methodology for how each field is sourced and updated.

Frequently Asked Questions

How do you spell "isomer"?
"isomer" is spelled I-S-O-M-E-R. The IPA pronunciation is /ˈaɪ.sə.mə/.
What does "isomer" mean?
As a noun, "isomer" means: Any of two or more compounds with the same molecular formula but with different structure.
How do you pronounce "isomer"?
The IPA (International Phonetic Alphabet) transcription for "isomer" is /ˈaɪ.sə.mə/. Click the speaker icon on the pronunciation badge above to hear it spoken aloud where audio is available.
What is the origin of the word "isomer"?
From iso- + -mer. See the full etymology section above for more details.
Is PlainSpell free to use?
Yes, PlainSpell is a completely free word reference. You can look up definitions, pronunciations, confusable pairs, homophones, and spelling corrections across 5 languages without any sign-up or subscription.

Using “isomer”

The practical upshot for anyone who landed here from a spell-check.

  • The one correct English spelling is I-S-O-M-E-R - every other letter order is a misspelling in standard orthography.
  • Say it as /ˈaɪ.sə.mə/ (IPA); tap the speaker on the pronunciation badge to hear it where audio exists.
  • Browse more English words and confusable pairs in the same reference. English words

Other uncommon English words near this rank

Data Source

Wiktionary (via kaikki.org), licensed under CC BY-SA & GFDL. Word ordering uses an open word-frequency list; misspelling variants are generated by edit-distance from the correct headword.

Source: Wiktionary (via kaikki.org) Structured Wiktionary extract

Source: FrequencyWords open word-frequency list FrequencyWords open word-frequency list