ill vs is, What's the Difference?

Which to use

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

#43,059
“ill” frequency rank: #2,727
“is” frequency rank: 45786
confusion score

Side-by-Side Comparison

Feature	ill	is
Definition	Enfermo.	Tercera persona del singular (he, she, it) del presente simple de be.

Where the eye mixes ill and is

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

3 ch

ill

2 ch

Why the eye confuses ill with is

These two trip readers on the page rather than in the ear: ill is /ɪl/ while is is /ɪz/. 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 verb), which is usually the fastest check. Our composite confusion score for this pair is 45786, 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/. is is at rank #2,727, tagged as averb, pronounced /ɪz/.

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 45786, this pair ranks #129,453 of 323,831 scored Spanish confusable pairs - roughly mid-pack for confusability.

Orthographic DNA of ill vs is

Shared letters: i. Private to "ill": l. Private to "is": s.

"ill" · 3 letters · shape VCC · "is" · 2 letters · shape VC

Frequently Asked Questions

Can "ill" and "is" be used interchangeably?

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

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

"is" is the more common of the two: it sits at frequency rank #2,727 in our Spanish list, against #43,059 for "ill". That is a wide gap, so in ordinary text the rarer spelling is the one worth double-checking.

What to do next

Pronunciation already separates them, if the page still looks alike, the dictionary links below settle it.

Full dictionary entry for "ill" with definition, IPA, and generated misspellings. Word entry
Full dictionary entry for "is" - compare definitions side by side with the headword page. Word entry
This pair ranks #129,453 of 323,831 scored Spanish confusable pairs in this corpus vintage. Corpus statistics
"ill" and "is" also get mixed up with nearby pairs, the highest-scored neighbour is "ill vs iza". Nearby pair

Confusion rank #129,453 of 323,831 scored Spanish pairs, corpus vintage 2026-09-03, not spelling advice.