This troublesome pair originated from the common misconception that there is such a word as stentorous, which is something to do with loud speaking or breathing. I’ve seen and heard this used, but in fact, it’s not a word at all! The word people are looking for there is stentorious, and the word they are probably being affected by when they think about it is stertorous.
Let’s sort out these two words that do actually exist, then.
Stentorious (or, indeed stentorian, which is listed in the Oxford Concise Dictionary at the expense of stentorious, but I reckon I’ve never come across) is used to describe a person’s voice, or the sound they emit, as being loud and powerful. Stentorious and stentorian are both listed in the Oxford Dictionaries online resource (which you can find here). I suppose stentorian might be marginally easier to spell, but in this case it seems a bit odd to have two words meaning exactly the same, even though I usually like that kind of thing.
Stertorous sounds pretty similar AND means a pretty similar (though not exactly matching) thing – it describes laboured and noisy breathing. I do like this distinction and think it’s important.
So stentorious or stentorian for vocal expression, stertorous for breathing, and stentorous for neither of them, because it doesn’t exist (but I bet a lot of people look it up!.
Do comment if you found this article because you looked up stentorous! Thank you!
You can find more troublesome pairs here, and here’s the index to them all!
LibroEditing proofreading, editing, transcription, localisation 
Steve Dunham
March 27, 2017 at 12:48 pm
Maybe it’s a transatlantic difference. I’ve heard “stentorian” now and then, but “stertorous” was new to me. I live in Virginia, USA.
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Liz Dexter
March 27, 2017 at 1:46 pm
It’s quite an obscure one, isn’t it – some people (ahem) thought stentorous existed, which it doens’t, having formed it carefully from stertorous. But when do we really use them?
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Cindy
March 29, 2019 at 12:12 am
We were reading Doña Barbara and he says “stertorous snoring” and we had a big argument about whether the translator mistranslated stentorian… this article was so helpful thank you.
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Liz Dexter
March 29, 2019 at 8:49 am
Oh, that’s very lovely to hear – thank you! Always glad to help!
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Corrine Daycock
May 24, 2019 at 9:07 pm
“Do comment if you found this article because you looked up stentorous! Thank you”
100% guilty!
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Liz Dexter
May 25, 2019 at 5:55 pm
Oh, funny – thanks for confessing!
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Dorothea
September 10, 2019 at 12:42 pm
No, the one I was looking for was stertorious! LOL!
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Liz Dexter
September 10, 2019 at 1:47 pm
Aha – excellent! So many versions!
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Karen Burbage
December 2, 2019 at 5:40 pm
You’re right! I was looking up “stentorous”! Never knew. Thank you for the enlightenment!
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Liz Dexter
December 2, 2019 at 5:55 pm
This does seem to chime with quite a few people!
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David Terrell
June 20, 2020 at 5:45 am
I saw the word stertorous in Mr Midshipman Hornblower (by CS Forrester) and wondered if it was related to a similar sounding word that means a loud and commanding voice, but I did not know quite how to spell it…stentorious. Just as you surmised …another “stentoran”.
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Liz Dexter
June 21, 2020 at 4:07 pm
Always glad to help!
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Tinderbox
January 1, 2024 at 8:45 pm
I was watching a police video where a man was overdosing, and the officer described his breathing as “heavy”. But “stentorious” leapt to my mind. I learn here that next time “stertorous” should leap to my mind instead.
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Liz Dexter
January 1, 2024 at 9:49 pm
Always glad to help!
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