S1 vs STS, What's the Difference?

Which to use

“S1” and “STS” are a confusable French pair: similar on the page, but distinct in meaning, check the gloss before you choose.

#23,361
“S1” frequency rank: #40,514
“STS” frequency rank: 63875
confusion score

Side-by-Side Comparison

Feature	S1	STS
Definition	Première vertèbre sacrale (de haut en bas).	Navette spatiale américaine ayant effectué 135 vols pour l'agence spatiale américaine (NASA) entre le 12 avril 1981 et juillet 2011.

Where the eye mixes S1 and STS

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

2 ch

3 ch

STS

Why the eye confuses S1 with STS

A purely visual mix-up. S1 (\ɛs.œ̃\) and STS (\ɛs te ɛs\) 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 63875, derived from the frequency rank of both members and their visual similarity.

S1 is recorded at frequency rank #23,361, classified as anoun, pronounced \ɛs.œ̃\. STS is at rank #40,514, tagged as anoun, pronounced \ɛs te ɛs\.

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 63875, this pair ranks #79,780 of 440,172 scored French confusable pairs - among the most confusable pairs.

Orthographic DNA of S1 vs STS

Shared letters: s. Private to "S1": -. Private to "STS": t.

"S1" · 1 letters · shape C · "STS" · 3 letters · shape CCC

Frequently Asked Questions

Can "S1" and "STS" be used interchangeably?

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

In ordinary French text, does "S1" or "STS" show up more?

"S1" is the more common of the two: it sits at frequency rank #23,361 in our French list, against #40,514 for "STS". The two are close in frequency, so neither is a safe default; check the meaning rather than guessing.

After this comparison

Eye-level mix-up between "S1" and "STS" is sorted above. Next: full entries or other pairs that share a letter shape.

Full dictionary entry for "S1" with definition, IPA, and generated misspellings. Word entry
Full dictionary entry for "STS" - compare definitions side by side with the headword page. Word entry
This pair ranks #79,780 of 440,172 scored French confusable pairs in this corpus vintage. Corpus statistics
"S1" and "STS" also get mixed up with nearby pairs, the highest-scored neighbour is "STS vs suu". Nearby pair

Confusion rank #79,780 of 440,172 scored French pairs, corpus vintage 2026-09-03, not spelling advice.