(Plural-monopuses, not monopi!)
1. An octopus with only one tentacle, also known as an eel. Not to be confused with a polypus, which is an octopus or any multi-tentacled animal. Monopuses are known for coming after people who do bad things.
2. Being too close to someone else in a drill move for marching band.
The monopuses are going to come get you!