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” has 13 generated spelling variants in the English index at frequency #8,741. The variants make it a useful spelling check.

#8,741
frequency rank, English
1,433
“U” headwords
13
tracked misspellings
4
confusable pairs

According to Wiktionary data (CC BY-SA, analyzed September 3, 2026) - Not stable.

Corpus desk

Index EN-unstable · unstable · English

unstable · rank #8,741 · 13 variants · 4 confusables

  • FREQ-COMMON #8,741
  • LEN-LONG 8 letters
  • VOW-3 3 vowels
  • CONFUS-MID 4 pairs
  • VAR-HIGH 13 variants
  • BOOK-MID 1,433
  • PHOTO-FINISH unified

Nearest frequency peer: unified (-1 rank slots)

Read with this headword: Spelling guide for this pattern

Desk codes from Wiktionary headword shape, FrequencyWords rank tier, confusable-pair count, generated misspelling depth, letter-cohort book size, and photo-finish peer. Not a difficulty grade.

Frequency neighbourhood for “unstable”

Lower corpus rank = more everyday usage (inverted bar length for readability)

corpus weight

What this shows Bars show where “unstable” sits against the nearest ranked English headwords in the FrequencyWords band, not a reprint of letter-browse containment.

Source FrequencyWords open word-frequency list As of September 3, 2026

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

This scale runs from the tiny cluster of words that carry ordinary speech (left) to the long tail of words almost nobody reaches for (right).unstablelands here:

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

Ticks step logarithmically, so each one marks a roughly tenfold drop in how often the word turns up. Same rarity band neighbours include “unified” (#8,740), “upstairs” (#8,742), “underway” (#8,739). Source: FrequencyWords open word-frequency list.

A misspelling magnet

The generator records 13 spelling variants around unstable (IPA /ʌnˈsteɪ.bəl/), anadjective. Corpus frequency is #8,741 among 1,433 “U” headwords. Wiktionary lists 7 senses, so context still picks the gloss.

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.

Recorded use

Wiktionary examples

These source excerpts show how unstable appears in context. They illustrate usage; the definition above remains the entry’s reference meaning.

  1. unstable foundation
  2. The structure is too unstable to stand safely.

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.

Similar English words by spelling shape

Same letter count and similar misspelling depth for "unstable", not the corpus desk frequency band.

Same letter count

Frequency-ranked English headwords with 8 letters (nearest by frequency rank).

upstairs#8,742underway#8,739uncommon#8,738autonomy#8,756

Similar misspelling depth

Headwords with a similar count of attested misspellings (13 here; floor ≥5).

seventeen13 variantsCanadians13 variantsproceeded13 variantspharmacy13 variants

What to do next

You've looked up "unstable". Here's where to go from here.

  • "unstable" maps to 4 confusable pairs in this vintage; the highest-scored is "usable". View pair
  • 13 edit-distance misspelling variants are generated for spell-check research on this headword. See variants
  • Usage frequency rank #8,741 among English headwords in this corpus. Corpus statistics
  • Browse more English words in the "U" letter cohort. U–Z browse
  • PlainSpell rotates a curated Word of the Day from the English corpus, a passive way to discover vocabulary. Word of the Day

PlainSpell is a reference corpus, not spelling advice. Verify unusual forms in context.

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