v. Slang 1. To make something dirty or contaminated, especially with mud, grime, or a similar substance: Don't step in that puddle; you'll muck up your shoes. The gears in the car's transmission were all mucked up.
2. To make some liquid unclear or unusable by stirring up elements settled on the bottom: Unfortunately, all the dredging in the river has mucked up the water so much that we can't go swimming. The rains mucked the water up, making it difficult for scuba divers to see.
3. To make something unusable by disrupting what should remain undisturbed: I tried to incorporate these ideas into my paper at the last minute, but all they did was to muck it up. The editor stopped the author from mucking up the book with needless revisions.