Quick answer
Mucus is the noun, the slimy substance itself. Mucous is the adjective that describes things related to it. Memory hook: the adjective has the extra -ous, just like nervous or jealous.
The core difference
Mucus is the slippery fluid, while mucous describes something that produces, contains or resembles it.
- mucus — the slippery fluid that lines the nose, throat and gut: A cold makes the body produce far more mucus than usual.
- mucous — relating to or resembling mucus: The mucous membrane lines the inside of your nose.
How to tell them apart
Ask yourself whether you need a thing or a description. If you are naming the substance, use mucus. If you are describing something else, such as a membrane, a coating or a gland, use mucous.
The mix-up appears most in health writing, where people write mucous for the fluid itself. Most other -ous words are adjectives too, so a noun ending in -ous should make you look twice.
Frequently asked questions
Is mucous a noun?
No, mucous is an adjective. The noun for the slimy fluid is mucus, with no o.
Which spelling goes with membrane?
Mucous membrane, because membrane is a thing being described. The fluid it produces is mucus.
Do the two words sound the same?
Yes, they are pronounced alike, which is why the spelling is so easy to confuse.
