1. To climb or clamber on(to) someone or something all at once or in a heap. We all piled on as soon as they opened the doors of the bus. The whole team piled onto the running back after he scored the winning touchdown. The kids piled on the bed to watch the scary movie together.

2. To load many people or things on(to) someone or something all at once or in a heap. In this usage, a noun or pronoun is used between "pile" and "on(to)." He just kept piling the papers on my desk throughout the day. We had to pile everyone onto the tour bus in a hurry so that they didn't miss the reservation. The wagon was already full of produce, but the pickers just kept piling it on.

3. To continue to increase or add up against someone or something. Typically used in reference to evidence, accusations, criticisms, etc. Now that one person has come forward to accuse him of embezzlement, more and more testimony keeps piling on. Criticisms were piling onto the embattled CEO, until finally he was forced to resign from the company. With the amount of bad press that's been piling on the senator, you'd think he would avoid the public spotlight for a while.

4. To continue to uncover or direct negative or damaging things, such as evidence, accusations, criticisms, etc., against someone or something. In this usage, a noun or pronoun is used between "pile" and "on(to)." He's already been given a lecture by the teacher—there's no need to pile more on now. Investigators have continued piling evidence onto the alleged crime lord in an attempt to finally put him away once and for all.

5. To criticize or attack someone in speech or writing all at once or in great numbers. People from across the state have been piling onto me ever since I wrote my controversial opinion piece for the local paper. She's been through enough already—I don't think we need to pile on any further.