Which to use
“fou” is an adjective and “FSB” is a name - they look or sound alike but fill different roles in a sentence.
- #1,063
- “fou” frequency rank
- #45,626
- “FSB” frequency rank
- 46689
- confusion score
Side-by-Side Comparison
| Feature | fou | FSB |
|---|---|---|
| Definition | Qualifie une personne qui a perdu la raison, qui est atteinte d’aliénation mentale. | Service de renseignement de la Russie chargé des affaires de sécurité intérieure, successeur du service de la sécurité intérieure du KGB. |
Where the eye mixes fou and FSB
Muted = shared; highlighted = the visual trap. They share 1 letter in sequence.
Why the eye confuses fou with FSB
These two trip readers on the page rather than in the ear: fou is \fu\ while FSB is \ɛf.ɛs.be\. 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 (adjective vs name), which is usually the fastest check. Our composite confusion score for this pair is 46689, derived from the frequency rank of both members and their visual similarity.
fou is recorded at frequency rank #1,063, classified as anadj, pronounced \fu\. FSB is at rank #45,626, tagged as aname, pronounced \ɛf.ɛs.be\.
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 46689, this pair ranks #192,916 of 440,172 scored French confusable pairs - roughly mid-pack for confusability.
Orthographic DNA of fou vs FSB
Shared letters: f. Private to "fou": ou. Private to "FSB": bs.
"fou" · 3 letters · shape CVV · "FSB" · 3 letters · shape CCC
Frequently Asked Questions
Is swapping "fou" for "FSB" ever safe?
Frequency check: "fou" vs "FSB" - which ranks higher?
Useful next steps
Visual near-miss handled. Browse the word pages or a neighbour when the next look-alike shows up.
- Full dictionary entry for "fou" with definition, IPA, and generated misspellings. Word entry
- Full dictionary entry for "FSB" - compare definitions side by side with the headword page. Word entry
- This pair ranks #192,916 of 440,172 scored French confusable pairs in this corpus vintage. Corpus statistics
- "fou" and "FSB" also get mixed up with nearby pairs, the highest-scored neighbour is "Fee vs FSB". Nearby pair
Confusion rank #192,916 of 440,172 scored French pairs, corpus vintage 2026-09-03, not spelling advice.