Which to use
“infirm” is an adjective and “infra” is an adverb - they look or sound alike but fill different roles in a sentence.
- #46,546
- “infirm” frequency rank
- #32,864
- “infra” frequency rank
- 79410
- confusion score
Side-by-Side Comparison
| Feature | infirm | infra |
|---|---|---|
| Definition | Weak or ill, not in good health. | Discussed later. |
Where the eye mixes infirm and infra
Muted = shared; highlighted = the visual trap. They share 4 letters in sequence. infirm runs 6 letters (VCCVCC) against infra's 5 (VCCCV) - the length gap alone is often enough to separate them once you know to check it.
Visual trap between infirm and infra
These two trip readers on the page rather than in the ear: infirm is /ɪnˈfɜːm/ while infra is /ˈɪn.fɹə/. Spoken aloud the problem disappears. In writing it persists, because they differ by 1 letter(s) in length, and the parts of speech differ too (adjective vs adverb), which is usually the fastest check. Our composite confusion score for this pair is 79410, derived from the frequency rank of both members and their visual similarity.
infirm is recorded at frequency rank #46,546, classified as anadj, pronounced /ɪnˈfɜːm/. infra is at rank #32,864, tagged as anadv, pronounced /ˈɪn.fɹə/.
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 79410, this pair ranks #22,151 of 530,003 scored English confusable pairs - among the most confusable pairs.
Orthographic DNA of infirm vs infra
Shared letters: finr. Private to "infirm": m. Private to "infra": a.
"infirm" · 6 letters · shape VCCVCC · "infra" · 5 letters · shape VCCCV
Known mistypes of this pair
Frequently Asked Questions
Can "infirm" and "infra" be used interchangeably?
Which is more common, "infirm" or "infra"?
Useful next steps
Eye-level mix-up between "infirm" and "infra" is sorted above. Next: full entries or other pairs that share a letter shape.
- Full dictionary entry for "infirm" with definition, IPA, and generated misspellings. Word entry
- Full dictionary entry for "infra" - compare definitions side by side with the headword page. Word entry
- This pair ranks #22,151 of 530,003 scored English confusable pairs in this corpus vintage. Corpus statistics
- "infirm" and "infra" also get mixed up with nearby pairs, the highest-scored neighbour is "infill vs infirm". 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 #22,151 of 530,003 scored English pairs, corpus vintage 2026-09-03, not spelling advice.