I haven’t posted a Troublesome Pair for ages but I’ve had this one up my sleeve (erm, no, I haven’t, that would be disgusting!) for ages and hadn’t got round to posting it. With a Birmingham Cough going the rounds still, this seemed a seasonal post; my apologies to the more sensitive reader. It is a valid and troublesome pair, though!
Mucus is the noun, i.e. the thing itself: slimy stuff that gets secreted by animals and even plants (it’s more commonly known as mucilage in plants, though mucilage is also, in general a viscous bodily fluid or secretion).
Mucous is the adjective – so mucous membranes secrete mucus, for example.
Bonus word: mucilaginous is the adjective that goes with mucilage. I bet you’re glad you asked, aren’t you!
You can find more troublesome pairs here, and here’s the index to them all!
LibroEditing proofreading, editing, transcription, localisation 
kaggsysbookishramblings
February 22, 2017 at 10:33 am
Eeek! Informative – though I often find myself cursing mucus and wondering why the body produces so much of it….
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Liz Dexter
February 23, 2017 at 7:43 am
Indeed, indeed. But an important distinction to know.
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Rebecca Foster
February 22, 2017 at 5:09 pm
And here I thought it was just a US/UK difference like tumor/tumour. Very helpful to know about the adjectival form. I love your series — it’s so thorough!
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Liz Dexter
February 23, 2017 at 7:40 am
So glad this has proved useful!
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Don Massenzio
February 23, 2017 at 4:28 pm
Reblogged this on Don Massenzio's Blog and commented:
Check out this helpful hint on the difference between Mucus and Mucous from the Libro Editing blog.
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aladybird
April 13, 2017 at 10:24 am
It isn’t always about UK vs US spellings, is it… Thanks for writing about another (really) troublesome pair. I’ve shared it via LinkedIn.
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Liz Dexter
April 13, 2017 at 11:10 am
Yes, that’s right. And thank you for sharing it!
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