AD vs AU, What's the Difference?

Which to use

“AD” is an adverb and “AU” is a noun - they look or sound alike but fill different roles in a sentence.

#1,779
“AD” frequency rank: #6,867
“AU” frequency rank: 8646
confusion score

Side-by-Side Comparison

Feature	AD	AU
Definition	Initialism of Anno Domini (borrowed from Latin); in the year of our Lord.	Initialism of alopecia universalis.

Letter map: AD vs AU

Shared letters muted; letters that set AD and AU apart highlighted. Shared run: 1.

2 ch

Part-of-speech tell for AD / AU

Our dataset has no pronunciation recorded for both members, so the reliable separator here is grammatical: AD is anadverb and AUanoun. On the page they differ by a single letter - d in “AD” becomes u in “AU”. Our composite confusion score for this pair is 8646, derived from the frequency rank of both members and their visual similarity.

AD is recorded at frequency rank #1,779, classified as anadv, pronounced /ˌeɪˈdi/. AU is at rank #6,867, tagged as anoun.

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 8646, this pair ranks #501,452 of 530,003 scored English confusable pairs - a relatively easy-to-tell-apart pair.

Orthographic DNA of AD vs AU

Shared letters: a. Private to "AD": d. Private to "AU": u.

"AD" · 2 letters · shape VC · "AU" · 2 letters · shape VV

Frequently Asked Questions

Is swapping "AD" for "AU" ever safe?

No - they are not even the same part of speech. "AD" is an adverb and "AU" a noun, so a sentence built for one is usually ungrammatical with the other.

Which is more common, "AD" or "AU"?

"AD" is the more common of the two: it sits at frequency rank #1,779 in our English list, against #6,867 for "AU". The two are close in frequency, so neither is a safe default; check the meaning rather than guessing.

What to do next

You've compared "AD" and "AU". Here's where to go from here.

Full dictionary entry for "AD" with definition, IPA, and generated misspellings. Word entry
Full dictionary entry for "AU" - compare definitions side by side with the headword page. Word entry
This pair ranks #501,452 of 530,003 scored English confusable pairs in this corpus vintage. Corpus statistics
"AD" and "AU" also get mixed up with nearby pairs, the highest-scored neighbour is "amb vs AU". Nearby pair

Confusion rank #501,452 of 530,003 scored English pairs, corpus vintage 2026-09-03, not spelling advice.