sei vs su, What's the Difference?

Which to use

“sei” and “su” are a confusable French pair: similar on the page, but distinct in meaning, check the gloss before you choose.

#36,154
“sei” frequency rank: #1,609
“su” frequency rank: 37763
confusion score

Side-by-Side Comparison

Feature	sei	su
Definition	Deuxième personne du singulier de l’impératif présent de sein.	Participe passé masculin singulier du verbe savoir.

Where the eye mixes sei and su

Muted = shared; highlighted = the visual trap. They share 1 letter in sequence.

3 ch

sei

2 ch

Visual trap between sei and su

A purely visual mix-up. sei (\zaɪ̯\) and su (\sy\) 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 1 letter(s) in length. Our composite confusion score for this pair is 37763, derived from the frequency rank of both members and their visual similarity.

sei is recorded at frequency rank #36,154, classified as averb, pronounced \zaɪ̯\. su is at rank #1,609, tagged as averb, pronounced \sy\.

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 37763, this pair ranks #260,094 of 440,172 scored French confusable pairs - roughly mid-pack for confusability.

Orthographic DNA of sei vs su

Shared letters: s. Private to "sei": ei. Private to "su": u.

"sei" · 3 letters · shape CVV · "su" · 2 letters · shape CV

Frequently Asked Questions

Is swapping "sei" for "su" ever safe?

No. They are said differently (\zaɪ̯\ versus \sy\) and carry different meanings; reading the sentence aloud is usually enough to catch the wrong one.

In ordinary French text, does "sei" or "su" show up more?

"su" is the more common of the two: it sits at frequency rank #1,609 in our French list, against #36,154 for "sei". That is a wide gap, so in ordinary text the rarer spelling is the one worth double-checking.

Useful next steps

Eye-level mix-up between "sei" and "su" is sorted above. Next: full entries or other pairs that share a letter shape.

Full dictionary entry for "sei" with definition, IPA, and generated misspellings. Word entry
Full dictionary entry for "su" - compare definitions side by side with the headword page. Word entry
This pair ranks #260,094 of 440,172 scored French confusable pairs in this corpus vintage. Corpus statistics
"sei" and "su" also get mixed up with nearby pairs, the highest-scored neighbour is "sei vs suu". Nearby pair

Confusion rank #260,094 of 440,172 scored French pairs, corpus vintage 2026-09-03, not spelling advice.