Which to use
“firth” is a noun and “forty” is a num - they look or sound alike but fill different roles in a sentence.
- #22,972
- “firth” frequency rank
- #5,130
- “forty” frequency rank
- 28102
- confusion score
Side-by-Side Comparison
| Feature | firth | forty |
|---|---|---|
| Definition | An arm or inlet of the sea; a river estuary. | The cardinal number occurring after thirty-nine and before forty-one, represented in Roman numerals as XL and in Arabic numerals as 40. |
Where the eye mixes firth and forty
Muted = shared; highlighted = the visual trap. They share 3 letters in sequence.
Why the eye confuses firth with forty
These two trip readers on the page rather than in the ear: firth is /fɜːθ/ while forty is /ˈfɔːti/. Spoken aloud the problem disappears. In writing it persists, because they share most of their letters but differ in 2 positions, and the parts of speech differ too (noun vs num), which is usually the fastest check. Our composite confusion score for this pair is 28102, derived from the frequency rank of both members and their visual similarity.
firth is recorded at frequency rank #22,972, classified as anoun, pronounced /fɜːθ/. forty is at rank #5,130, tagged as anum, pronounced /ˈfɔːti/.
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 28102, this pair ranks #373,727 of 530,003 scored English confusable pairs - roughly mid-pack for confusability.
Orthographic DNA of firth vs forty
Shared letters: frt. Private to "firth": hi. Private to "forty": oy.
"firth" · 5 letters · shape CVCCC · "forty" · 5 letters · shape CVCCV
Known mistypes of this pair
Frequently Asked Questions
Do "firth" and "forty" mean the same thing in a sentence?
Frequency check: "firth" vs "forty" - which ranks higher?
What to do next
Visual near-miss handled. Browse the word pages or a neighbour when the next look-alike shows up.
- Full dictionary entry for "firth" with definition, IPA, and generated misspellings. Word entry
- Full dictionary entry for "forty" - compare definitions side by side with the headword page. Word entry
- This pair ranks #373,727 of 530,003 scored English confusable pairs in this corpus vintage. Corpus statistics
- "firth" and "forty" also get mixed up with nearby pairs, the highest-scored neighbour is "firth vs frith". 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 #373,727 of 530,003 scored English pairs, corpus vintage 2026-09-03, not spelling advice.