Which to use
“STI” is a noun and “stiff” is an adjective - they look or sound alike but fill different roles in a sentence.
- #26,266
- “STI” frequency rank
- #8,357
- “stiff” frequency rank
- 34623
- confusion score
Side-by-Side Comparison
| Feature | STI | stiff |
|---|---|---|
| Definition | Initialism of sexually transmitted infection (also S.T.I.). | Rigid; hard to bend; inflexible. |
Letter map: STI vs stiff
Shared letters muted; letters that set STI and stiff apart highlighted. Shared run: 3.
Part-of-speech tell for STI / stiff
Our dataset has no pronunciation recorded for both members, so the reliable separator here is grammatical: STI is anoun and stiffanadjective. On the page they differ by 2 extra letter(s) - “STI” sits inside “stiff”. Our composite confusion score for this pair is 34623, derived from the frequency rank of both members and their visual similarity.
STI is recorded at frequency rank #26,266, classified as anoun. stiff is at rank #8,357, tagged as anadj, pronounced /stɪf/.
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 34623, this pair ranks #319,180 of 530,003 scored English confusable pairs - roughly mid-pack for confusability.
Orthographic DNA of STI vs stiff
Shared letters: ist. Private to "STI": -. Private to "stiff": f.
"STI" · 3 letters · shape CCV · "stiff" · 5 letters · shape CCVCC
Known mistypes of this pair
- stiff ← sitff · sstiff · stfif · stif · sttiff · tsiff
Frequently Asked Questions
Do "STI" and "stiff" mean the same thing in a sentence?
Frequency check: "STI" vs "stiff" - which ranks higher?
After this comparison
You've compared "STI" and "stiff". Here's where to go from here.
- Full dictionary entry for "STI" with definition, IPA, and generated misspellings. Word entry
- Full dictionary entry for "stiff" - compare definitions side by side with the headword page. Word entry
- This pair ranks #319,180 of 530,003 scored English confusable pairs in this corpus vintage. Corpus statistics
- "STI" and "stiff" also get mixed up with nearby pairs, the highest-scored neighbour is "Sif vs STI". 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 #319,180 of 530,003 scored English pairs, corpus vintage 2026-09-03, not spelling advice.