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 spellings diverge
Shared letters are muted; the letters that actually set filth and firth apart are highlighted. They share 4 letters in sequence, which is exactly why the eye skips the difference.
Spelling & Dictionary Insight
filth and firth 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 a single letter - l in “filth” becomes r in “firth” - close enough that the eye skips over the difference, far enough that meaning fully diverges. 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.
Frequency comparison
Frequently Asked Questions
Can "filth" and "firth" be used interchangeably?
Remembering filth vs firth
The fastest way to pick the right one every time.
- Read both glosses above and match the meaning you intend, only context separates this pair.
- See each word in full, definition, IPA, etymology and its other confusables. Full “filth” entry
- Browse more pairs most likely to be confused. Most confusable