ad vs aux, What's the Difference?

Which to use

“ad” is a noun and “aux” is a contraction - they look or sound alike but fill different roles in a sentence.

#5,365
“ad” frequency rank: #32,511
“aux” frequency rank: 37876
confusion score

Side-by-Side Comparison

Feature	ad	aux
Definition	Nombre.	Contracción de la preposición à y el artículo les; a las ; a los.

Where the eye mixes ad and aux

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

2 ch

3 ch

aux

Why the eye confuses ad with aux

These two trip readers on the page rather than in the ear: ad is [ɑd] while aux is /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 (noun vs contraction), which is usually the fastest check. Our composite confusion score for this pair is 37876, derived from the frequency rank of both members and their visual similarity.

ad is recorded at frequency rank #5,365, classified as anoun, pronounced [ɑd]. aux is at rank #32,511, tagged as acontraction, pronounced /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 37876, this pair ranks #173,002 of 323,831 scored Spanish confusable pairs - roughly mid-pack for confusability.

Orthographic DNA of ad vs aux

Shared letters: a. Private to "ad": d. Private to "aux": ux.

"ad" · 2 letters · shape VC · "aux" · 3 letters · shape VVC

Frequently Asked Questions

Is swapping "ad" for "aux" ever safe?

No - they are not even the same part of speech. "ad" is a noun and "aux" a contraction, so a sentence built for one is usually ungrammatical with the other.

In ordinary Spanish text, does "ad" or "aux" show up more?

"ad" is the more common of the two: it sits at frequency rank #5,365 in our Spanish list, against #32,511 for "aux". The two are close in frequency, so neither is a safe default; check the meaning rather than guessing.

After this comparison

Visual near-miss handled. Browse the word pages or a neighbour when the next look-alike shows up.

Full dictionary entry for "ad" with definition, IPA, and generated misspellings. Word entry
Full dictionary entry for "aux" - compare definitions side by side with the headword page. Word entry
This pair ranks #173,002 of 323,831 scored Spanish confusable pairs in this corpus vintage. Corpus statistics
"ad" and "aux" also get mixed up with nearby pairs, the highest-scored neighbour is "atl vs aux". Nearby pair

Confusion rank #173,002 of 323,831 scored Spanish pairs, corpus vintage 2026-09-03, not spelling advice.