mucous

The word "mucous" describes something that is related to mucus or to the membranes that make it. These membranes line parts of the body such as the nose, mouth, lungs, and digestive tract, where they help keep surfaces moist and protected. So when someone says "mucous membrane," they mean the soft, wet lining inside those parts of the body.

This word is often mixed up with "mucus." The difference is simple: "mucus" is the substance, but "mucous" describes things connected to that substance. You can have mucus in your nose, and that mucus comes from a mucous membrane.

The word "mucous" is an adjective. It describes something that has to do with mucus or with the membranes that produce mucus. These membranes are found in places like the nose, mouth, throat, lungs, and digestive system. They form a soft, wet lining that helps protect the body and keep those surfaces from drying out.

People often confuse "mucous" with "mucus" because the words look so similar. The key difference is that "mucus" is a noun, meaning the slippery substance itself, while "mucous" is used to describe related tissue, surfaces, or discharge. For example, you might talk about a mucous membrane in the nose, a mucous lining in the stomach, or mucous secretions from the throat.

This adjective is mostly used in medical or body-related contexts. A doctor may check whether the mucous membranes are dry, swollen, pale, or irritated. In that kind of sentence, the word points to the body lining that makes and holds mucus, not to the substance alone.

So if "mucus" is the slimy material, "mucous" is the word that describes what is connected to it. That is why "mucous membrane" is correct, while "mucus membrane" is not.