ill vs io, What's the Difference?

Which to use

“ill” is an adjective and “io” is a pronoun - they look or sound alike but fill different roles in a sentence.

#43,059
“ill” frequency rank: #9,480
“io” frequency rank: 52539
confusion score

Side-by-Side Comparison

Feature	ill	io
Definition	Enfermo.	Algo.

Where the eye mixes ill and io

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

3 ch

ill

2 ch

Why the eye confuses ill with io

These two trip readers on the page rather than in the ear: ill is /ɪl/ while io is /ˈi.o/. 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 pronoun), which is usually the fastest check. Our composite confusion score for this pair is 52539, derived from the frequency rank of both members and their visual similarity.

ill is recorded at frequency rank #43,059, classified as anadj, pronounced /ɪl/. io is at rank #9,480, tagged as apron, pronounced /ˈi.o/.

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 52539, this pair ranks #92,202 of 323,831 scored Spanish confusable pairs - roughly mid-pack for confusability.

Orthographic DNA of ill vs io

Shared letters: i. Private to "ill": l. Private to "io": o.

"ill" · 3 letters · shape VCC · "io" · 2 letters · shape VV

Frequently Asked Questions

Is swapping "ill" for "io" ever safe?

No - they are not even the same part of speech. "ill" is an adjective and "io" a pronoun, so a sentence built for one is usually ungrammatical with the other.

Frequency check: "ill" vs "io" - which ranks higher?

"io" is the more common of the two: it sits at frequency rank #9,480 in our Spanish list, against #43,059 for "ill". The two are close in frequency, so neither is a safe default; check the meaning rather than guessing.

Useful next steps

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

Full dictionary entry for "ill" with definition, IPA, and generated misspellings. Word entry
Full dictionary entry for "io" - compare definitions side by side with the headword page. Word entry
This pair ranks #92,202 of 323,831 scored Spanish confusable pairs in this corpus vintage. Corpus statistics
"ill" and "io" also get mixed up with nearby pairs, the highest-scored neighbour is "ill vs iza". Nearby pair

Confusion rank #92,202 of 323,831 scored Spanish pairs, corpus vintage 2026-09-03, not spelling advice.