Gunk (noun)

1. A sticky, dirty, or thick substance that is difficult to remove.
2. A substance that is considered unwanted or dirty.

Origin:

Originated as slang, it may be derived from the word gunk, meaning "to vomit," or from the word gunk, meaning "a sticky, gooey substance".

Examples:

1. The engine was covered in gunk and needed to be cleaned.
2. He had to remove the gunk from the gears before it could be used again.
3. The gunk in the pipe caused a blockage.
4. He scraped the gunk off the pan.
5. The gunk on the windshield made it hard to see.