unstable

/ʌnˈsteɪ.bəl/

//ʌnˈsteɪ.bəl// adj

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

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

The verdict

“unstable” is a regularly-used English word, ranked #8,741 in English word frequency and used as an adjective.

#8,741
frequency rank, English
8
letters
13
tracked misspellings
4
confusable pairs

According to Wiktionary data (CC BY-SA, analyzed May 6, 2026) - Not stable.

Visual similarity to commonly confused words

How many letter changes separate each confused pair (Levenshtein distance, normalized).

unstable vs usable
75% similar
unstable vs unusable
75% similar
unstable vs unsuitable
80% similar

Source: PlainSpell confusable corpus (Wiktionary, CC BY-SA).

Key facts for unstable
PropertyValue
Headwordunstable
LanguageEnglish
Part of speechAdjective
IPA/ʌnˈsteɪ.bəl/
Letters8
Frequency rank#8,741
Misspellings tracked13
Confusable pairs4
SourceWiktionary (kaikki.org)

Where “unstable” 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). unstable lands here:

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

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

Spelling & Dictionary Insight

The English entry for unstable is 8 letters long, classified as an adjective, and transcribed in the International Phonetic Alphabet as /ʌnˈsteɪ.bəl/. Corpus data places it at rank #8,741 in overall English word frequency, indicating it appears regularly in written and spoken text. Wiktionary records 7 distinct senses for this headword, so context determines which meaning a reader should apply.

Our generated misspelling index lists 13 likely wrong-spelling variants for unstable, with forms such as "nustable", "unnstable", and "unsatble". Each of these forms differs from the correct spelling by one small edit: a doubled letter, a dropped silent letter, or a substituted vowel. It also participates in 4 confusable-pair relationships, "usable", "unusable", "unsuitable", and more, since the words sound or look close enough that writers reach for the wrong one mid-sentence.

Etymologically, the entry records: From Middle English unstable; equivalent to un- (not) + stable. The correct English form is unstable, spelled U-N-S-T-A-B-L-E.

Definition

  1. 1
    Not stable.
  2. 2
    Having a strong tendency to change.
  3. 3
    Fluctuating; not constant.
  4. 4
    Fickle.
  5. 5
    Unpredictable.
  6. 6
    Readily decomposable.
  7. 7
    Radioactive, especially with a short half-life.

Etymology

From Middle English unstable; equivalent to un- (not) + stable.

Synonyms

labileinstableunsteadyarbitrarycapricioustotteringwobblyrickety

Antonyms

stable

This word in other languages

inestable(Español)instable(Français)instabil(Deutsch)instável(Português)

Common misspellings

Also misspelled as: nustable,unnstable,unsatble,unsstable,unstabble,unstabel,unstablle,unstalbe,unstbale,unstible,unsttable,untsable,usntable

Misspelling Pattern Breakdown

How far each generated variant is from the correct spelling of unstable - expressed in single-character edits (insert, delete, or swap one letter). Bigger bars stand out at a glance; a one-edit slip is the hardest to catch.

nustable2unnstable1unsatble2unsstable1unstabble1unstabel2unstablle1unstalbe2
Edit distance from "unstable"

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 "unstable"?
"unstable" is spelled U-N-S-T-A-B-L-E. The IPA pronunciation is /ʌnˈsteɪ.bəl/.
What does "unstable" mean?
As an adjective, "unstable" means: Not stable.
What words are commonly confused with "unstable"?
"unstable" is commonly confused with "usable", "unusable", "unsuitable". These words look or sound similar but have different meanings. PlainSpell provides detailed comparisons for each pair.
How do you pronounce "unstable"?
The IPA (International Phonetic Alphabet) transcription for "unstable" is /ʌnˈsteɪ.bəl/. 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 "unstable"?
From Middle English unstable; equivalent to un- (not) + stable. 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 “unstable”

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

  • The one correct English spelling is U-N-S-T-A-B-L-E - every other letter order is a misspelling in standard orthography.
  • Say it as /ʌnˈsteɪ.bəl/ (IPA); tap the speaker on the pronunciation badge to hear it where audio exists.
  • Don't mix it up with “usable” - see the side-by-side comparison. unstable vs usable
  • 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