Which to use
“undo” is a verb and “union” is a noun - they look or sound alike but fill different roles in a sentence.
- #13,631
- “undo” frequency rank
- #890
- “union” frequency rank
- 14521
- confusion score
Side-by-Side Comparison
| Feature | undo | union |
|---|---|---|
| Definition | To reverse the effects of an action. | The act of uniting or joining two or more things into one. |
Where the eye mixes undo and union
Muted = shared; highlighted = the visual trap. They share 3 letters in sequence.
Visual trap between undo and union
These two trip readers on the page rather than in the ear: undo is /ʌnˈduː/ while union is /ˈjuː.njən/. Spoken aloud the problem disappears. In writing it persists, because they differ by 1 letter(s) in length, and the parts of speech differ too (verb vs noun), which is usually the fastest check. Our composite confusion score for this pair is 14521, derived from the frequency rank of both members and their visual similarity.
undo is recorded at frequency rank #13,631, classified as averb, pronounced /ʌnˈduː/. union is at rank #890, tagged as anoun, pronounced /ˈjuː.njən/.
Glosses for this pair are partially populated in our dataset, but the full side-by-side definitions above should still guide you to the right choice.
With a confusion score of 14521, this pair ranks #469,529 of 530,003 scored English confusable pairs - a relatively easy-to-tell-apart pair.
Orthographic DNA of undo vs union
Shared letters: nou. Private to "undo": d. Private to "union": i.
"undo" · 4 letters · shape VCCV · "union" · 5 letters · shape VCVVC
Known mistypes of this pair
Frequently Asked Questions
Is swapping "undo" for "union" ever safe?
In ordinary English text, does "undo" or "union" show up more?
Useful next steps
Eye-level mix-up between "undo" and "union" is sorted above. Next: full entries or other pairs that share a letter shape.
- Full dictionary entry for "undo" with definition, IPA, and generated misspellings. Word entry
- Full dictionary entry for "union" - compare definitions side by side with the headword page. Word entry
- This pair ranks #469,529 of 530,003 scored English confusable pairs in this corpus vintage. Corpus statistics
- "undo" and "union" also get mixed up with nearby pairs, the highest-scored neighbour is "UHD vs undo". Nearby pair
- Recorded mistypes exist for at least one side of this pair, useful when a spell-checker or OCR lands on the wrong form. See mistypes
Confusion rank #469,529 of 530,003 scored English pairs, corpus vintage 2026-09-03, not spelling advice.