ill vs io, What's the Difference?

Which to use

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

#44,899
“ill” frequency rank: #18,900
“io” frequency rank: 63799
confusion score

Side-by-Side Comparison

Feature	ill	io
Definition	doente	sempre

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/, /ˈi.ɔ/. 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 63799, derived from the frequency rank of both members and their visual similarity.

ill is recorded at frequency rank #44,899, classified as anadj, pronounced /ɪl/. io is at rank #18,900, tagged as anadv, pronounced /ˈi.o/, /ˈi.ɔ/.

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 63799, this pair ranks #6,030 of 75,631 scored Portuguese confusable pairs - among the most confusable pairs.

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" an adverb, 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 #18,900 in our Portuguese list, against #44,899 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 #6,030 of 75,631 scored Portuguese 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 ino". Nearby pair

Confusion rank #6,030 of 75,631 scored Portuguese pairs, corpus vintage 2026-09-03, not spelling advice.