Have you ever been confused by the two different spellings of "mucus" and "mucous"? Well, they seem to refer to the same thing, so why the one-letter distinction? Is it a classical situation of two accepted spellings for the same word, is there an older version or is simply one of them a misspelling?
You are about to get rid of all these doubts in a few seconds, because it's actually easy to remember and we'll quickly explain below why "mucus" and "mucous" are spelled differently.
Mucus vs. Mucous
The single difference between "mucus" and "mucous" is not in their meanings, but in their functions. They work as different parts of speech in a sentence. "Mucus" is a noun, referring to the actual concept that we understand through "mucus", while "mucous" is the adjective used to describe the same thing.
So...they actually refer to the same substance, the same body secretion, only that the first is a noun and the second is an adjective. It's as simple as that.
When do we use "mucus"?
"Mucus" is the thick liquid produced inside the nose, especially in case of congestion, or by other body parts. So the word is used when referring to this fluid.
Example: The presence of mucus and nasal congestion is clearly indicating he's got the flu. - "mucus" is the thick substance secreted inside the nose.
When do we use "mucous"?
"Mucous" is actually the adjective used while referring to the same thing as "mucus". So the word is mainly used when describing those body parts that actually secrete the "mucus".
Example: Mucous membranes are those that secrete mucus into your body. - "mucous" describes that body part that produces mucus.
There's not much philosophy behind these words - you don't have to be a doctor or medical specialist to remember and understand the explanation for their different spellings. "Mucus" is the noun defining the actual thick fluid secreted by the body, while "mucous" is the adjective describing a body part that produces the "mucus".