extension vs open, What's the Difference?

Which to use

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

#33,032
“extension” frequency rank: #2,607
“open” frequency rank: 35639
confusion score

Side-by-Side Comparison

Feature	extension	open
Definition	Ausdehnung, Erweiterung, Umfang	etwas ist nicht geschlossen

Letter map: extension vs open

Shared letters muted; letters that set extension and open apart highlighted. Shared run: 2.

9 ch

extension

4 ch

open

Grammar separator: extension vs open

Our dataset has no pronunciation recorded for both members, so the reliable separator here is grammatical: extension is anoun and openanadjective. On the page they differ by 5 letter(s) in length. Our composite confusion score for this pair is 35639, derived from the frequency rank of both members and their visual similarity.

extension is recorded at frequency rank #33,032, classified as anoun, pronounced […]. open is at rank #2,607, tagged as anadj, pronounced […].

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 35639, this pair ranks #1,635,197 of 2,006,359 scored German confusable pairs - a relatively easy-to-tell-apart pair.

Orthographic DNA of extension vs open

Shared letters: eno. Private to "extension": istx. Private to "open": p.

"extension" · 9 letters · shape VCCVCCVVC · "open" · 4 letters · shape VCVC

Known mistypes of this pair

extension ← etxension · exetnsion · extenison · extennsion · extensino · extensionn · extensoin · extenssion
open ← oepn · openn · opne · oppen · poen

Frequently Asked Questions

Is swapping "extension" for "open" ever safe?

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

In ordinary German text, does "extension" or "open" show up more?

"open" is the more common of the two: it sits at frequency rank #2,607 in our German list, against #33,032 for "extension". That is a wide gap, so in ordinary text the rarer spelling is the one worth double-checking.

Useful next steps

Done with this confusable. These links stay specific to "extension" and "open".

Full dictionary entry for "extension" with definition, IPA, and generated misspellings. Word entry
Full dictionary entry for "open" - compare definitions side by side with the headword page. Word entry
This pair ranks #1,635,197 of 2,006,359 scored German confusable pairs in this corpus vintage. Corpus statistics
"extension" and "open" also get mixed up with nearby pairs, the highest-scored neighbour is "extension vs puzzles". Nearby pair
Recorded mistypes exist for at least one side of this pair, useful when a spell-checker or OCR lands on the wrong form. See mistypes

Confusion rank #1,635,197 of 2,006,359 scored German pairs, corpus vintage 2026-09-03, not spelling advice.