Which to use
“filth” and “firth” are a confusable English pair: similar on the page, but distinct in meaning, check the gloss before you choose.
- #16,914
- “filth” frequency rank
- #22,972
- “firth” frequency rank
- 39886
- confusion score
Side-by-Side Comparison
| Feature | filth | firth |
|---|---|---|
| Definition | Dirt; foul matter; that which soils or defiles. | An arm or inlet of the sea; a river estuary. |
Where the eye mixes filth and firth
Muted = shared; highlighted = the visual trap. They share 4 letters in sequence. filth and firth follow the identical consonant-vowel pattern (CVCCC). Same shape at a glance is often the real trap, independent of shared letters.
Visual trap between filth and firth
A purely visual mix-up. filth (/fɪlθ/) and firth (/fɜːθ/) are said differently, so reading them aloud is the quickest way to catch the wrong one. On the page they stay close: they differ by a single letter - l in “filth” becomes r in “firth”. Our composite confusion score for this pair is 39886, derived from the frequency rank of both members and their visual similarity.
filth is recorded at frequency rank #16,914, classified as anoun, pronounced /fɪlθ/. firth is at rank #22,972, tagged as anoun, pronounced /fɜːθ/.
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 39886, this pair ranks #272,587 of 530,003 scored English confusable pairs - roughly mid-pack for confusability.
Orthographic DNA of filth vs firth
Shared letters: fhit. Private to "filth": l. Private to "firth": r.
"filth" · 5 letters · shape CVCCC · "firth" · 5 letters · shape CVCCC
Known mistypes of this pair
Frequently Asked Questions
Can "filth" and "firth" be used interchangeably?
Frequency check: "filth" vs "firth" - which ranks higher?
What to do next
Pronunciation already separates them, if the page still looks alike, the dictionary links below settle it.
- Full dictionary entry for "filth" with definition, IPA, and generated misspellings. Word entry
- Full dictionary entry for "firth" - compare definitions side by side with the headword page. Word entry
- This pair ranks #272,587 of 530,003 scored English confusable pairs in this corpus vintage. Corpus statistics
- "filth" and "firth" 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 #272,587 of 530,003 scored English pairs, corpus vintage 2026-09-03, not spelling advice.