v.1. To arrange something into a pile: We piled up the firewood in the garage. I piled the dirty dishes up in the sink.
2. To accumulate: My bills piled up while I was in the hospital.
3. To cause something to accumulate: The company is piling up debt with its risky investments. The team piled 40 points up in the first half of the game.
4. To crash into each other; collide. Used especially of vehicles: Because of the thick fog, dozens of cars piled up on the freeway.