half-life

/ˈhæfˌlaɪf/

//ˈhæfˌlaɪf// noun

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

"half-life" is a 8-letter English headword indexed on PlainSpell.

The verdict

“half-life” is uncommon English (outside the top frequency list), classed as a noun. The kind of spelling people second-guess.

Unranked
below top-frequency English
9
letters

According to Wiktionary data (CC BY-SA, analyzed May 6, 2026) - The time required for half the nuclei in a sample of an isotope to undergo radioactive decay.

Key facts for half-life
PropertyValue
Headwordhalf-life
LanguageEnglish
Part of speechNoun
IPA/ˈhæfˌlaɪf/
Letters9
Misspellings tracked0
Confusable pairs0
SourceWiktionary (kaikki.org)

Where “half-life” sits in English frequency

half-life falls outside the top-100,000 ranked English words, the long-tail zone of technical, archaic, or low-frequency vocabulary, exactly where readers second-guess spellings most.

Beyond rank #100,000. Source: FrequencyWords open word-frequency list.

Rare enough to double-check

half-life is uncommon English outside the top frequency list, classed as anoun, transcribed /ˈhæfˌlaɪf/. Rarity is why readers land here mid-draft. 4 senses are on record.

half-life doesn't appear in our generated misspelling index, suggesting the orthography follows predictable English patterns. Our dataset records no confusable match here, which tends to mean the word is visually distinctive enough to stand on its own.

Etymologically, the entry records: From half- + life. The correct English form is half-life, spelled H-A-L-F---L-I-F-E.

Definition

  1. 1
    The time required for half the nuclei in a sample of an isotope to undergo radioactive decay.
  2. 2
    In a chemical reaction, the time required for the concentration of a reactant to fall from a chosen value to half that value.
  3. 3
    The time it takes for a substance (drug, radioactive nuclide, or other) to lose half of its pharmacological, physiologic, or radiological activity.
  4. 4
    The amount of time it takes for an idea or a fashion to lose half of its influential power.

Etymology

From half- + life.

This word in other languages

demi-vie(Français)Halbwertszeit(Deutsch)

Definitions, pronunciation, and etymology for this entry are drawn from Wiktionary via the kaikki.org structured extract (CC BY-SA). See the methodology for how each field is sourced and updated.

Frequently Asked Questions

How do you spell "half-life"?
"half-life" is spelled H-A-L-F---L-I-F-E. The IPA pronunciation is /ˈhæfˌlaɪf/.
What does "half-life" mean?
As a noun, "half-life" means: The time required for half the nuclei in a sample of an isotope to undergo radioactive decay.
How do you pronounce "half-life"?
The IPA (International Phonetic Alphabet) transcription for "half-life" is /ˈhæfˌlaɪf/. 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 "half-life"?
From half- + life. 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 “half-life”

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

  • The one correct English spelling is H-A-L-F---L-I-F-E - every other letter order is a misspelling in standard orthography.
  • Say it as /ˈhæfˌlaɪf/ (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
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