undecidable
"undecidable" is a 11-letter English headword indexed on PlainSpell.
The verdict
“undecidable” is uncommon English (outside the top frequency list), classed as an adjective. The kind of spelling people second-guess.
- Unranked
- below top-frequency English
- 11
- letters
According to Wiktionary data (CC BY-SA, analyzed September 3, 2026) - Incapable of being algorithmically decided in finite time. For example, a set of strings is undecidable if it is impossible to program a computer (even one with infinite memory) to determine whethe...
Corpus desk
Index EN-undecidable · undecidable · English
undecidable · unranked · 0 variants · 0 confusables
- FREQ-UNRANKED Unranked
- LEN-MEGA 11 letters
- VOW-5 5 vowels
- CONFUS-0 No pairs
- VAR-0 0 variants
- BOOK-THIN "U" thin
- PHOTO-UNK Peer pending
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.
| Property | Value |
|---|---|
| Headword | undecidable |
| Language | English |
| Part of speech | Adjective |
| Letters | 11 |
| Misspellings tracked | 0 |
| Confusable pairs | 0 |
| Source | Wiktionary (kaikki.org) |
Long-tail rank of “undecidable” in English
Rare enough to double-check
undecidable is uncommon English outside the top frequency list, classed as anadjective. Rarity is why readers land here mid-draft. 2 senses are on record.
The misspelling generator found no plausible variants for undecidable, and the word's spelling is regular enough that our generator found nothing worth flagging. Our confusable-pair dataset has no match for it, which tends to mean the word is visually distinctive enough to stand on its own.
Etymologically, the entry records: From un- + decidable. The correct English form is undecidable, spelled U-N-D-E-C-I-D-A-B-L-E.
Definition
- 1Incapable of being algorithmically decided in finite time. For example, a set of strings is undecidable if it is impossible to program a computer (even one with infinite memory) to determine whether or not specified strings are included.
- 2(of a WFF) logically independent from the axioms of a given theory; i.e., that it can never be either proved or disproved (i.e., have its negation proved) on the basis of the axioms of the given theory. (Note: this latter definition is independent of any time bounds or computability issues, i.e., more Platonic.)
Recorded use
Wiktionary exampleThese source excerpts show how undecidable appears in context. They illustrate usage; the definition above remains the entry’s reference meaning.
The first-order procedure SP differs from the proposi- tional procedure CP°₁ in an essential feature. Namely, CP°₁ always terminates while SP may run forever as we have seen with the example immediately after (3.7). This is not a specific defect of SP. Rather it is known that first-order logic is an undecidable theory while propositional logic is a decida…
Etymology
From un- + decidable.
Antonyms
This word in other languages
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.