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 |
Where the spellings diverge
Shared letters are muted; the letters that actually set undefined and underlined apart are highlighted. They share 8 letters in sequence, which is exactly why the eye skips the difference.
Spelling & Dictionary Insight
undefined and underlined form a confusable pair in the English index, two distinct headwords that are easily confused because they look alike, sound alike, or both. They differ by 1 letter(s) in length - close enough that the eye skips over the difference, far enough that meaning fully diverges. 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.
Frequency comparison
Frequently Asked Questions
Can "undefined" and "underlined" be used interchangeably?
Remembering undefined vs underlined
The fastest way to pick the right one every time.
- Check the role first: if you need an adjective, it's “undefined”; for a verb, it's “underlined”.
- See each word in full, definition, IPA, etymology and its other confusables. Full “undefined” entry
- Browse more pairs most likely to be confused. Most confusable