Which to use
“undefined” is an adjective and “underlined” is a verb - they look or sound alike but fill different roles in a sentence.
- #27,687
- “undefined” frequency rank
- #25,629
- “underlined” frequency rank
- 53316
- confusion score
Side-by-Side Comparison
| Feature | undefined | underlined |
|---|---|---|
| Definition | Lacking a definition or value. | simple past and past participle of underline |
Letter map: undefined vs underlined
Shared letters muted; letters that set undefined and underlined apart highlighted. Shared run: 8.
Grammar separator: undefined vs underlined
Our dataset has no pronunciation recorded for both members, so the reliable separator here is grammatical: undefined is anadjective and underlinedaverb. On the page they differ by 1 letter(s) in length. Our composite confusion score for this pair is 53316, derived from the frequency rank of both members and their visual similarity.
undefined is recorded at frequency rank #27,687, classified as anadj. underlined is at rank #25,629, tagged as averb.
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 53316, this pair ranks #149,962 of 530,003 scored English confusable pairs - roughly mid-pack for confusability.
Orthographic DNA of undefined vs underlined
Shared letters: deinu. Private to "undefined": f. Private to "underlined": lr.
"undefined" · 9 letters · shape VCCVCVCVC · "underlined" · 10 letters · shape VCCVCCVCVC
Known mistypes of this pair
- undefined ← nudefined · udnefined · unddefined · undeffined · undefiend · undefinde · undefinedd · undefinned
- underlined ← nuderlined · udnerlined · undderlined · undelrined · underilned · underliend · underlinde · underlinedd
Frequently Asked Questions
Can "undefined" and "underlined" be used interchangeably?
Frequency check: "undefined" vs "underlined" - which ranks higher?
After this comparison
Done with this confusable. These links stay specific to "undefined" and "underlined".
- Full dictionary entry for "undefined" with definition, IPA, and generated misspellings. Word entry
- Full dictionary entry for "underlined" - compare definitions side by side with the headword page. Word entry
- This pair ranks #149,962 of 530,003 scored English confusable pairs in this corpus vintage. Corpus statistics
- "undefined" and "underlined" also get mixed up with nearby pairs, the highest-scored neighbour is "underlined vs undersized". 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 #149,962 of 530,003 scored English pairs, corpus vintage 2026-09-03, not spelling advice.