1. To exploit someone's trust for one's own purpose, gain, or agenda; to harm someone through deceit or treachery. Senator Davis was supposed to be working with me to bridge the gap between Democrats and Republicans on the issue of gun control, but, instead, she threw me under the bus to get a boost in the polls with her constituency. The investment company threw its clients under the bus when it chose to redirect their hard earned money into various Ponzi schemes that benefited only a few board members at the top.

2. To avoid blame, trouble, or criticism by allowing someone else to take responsibility. Tommy was caught with the marijuana in his backpack, but he threw me under the bus and said it belonged to me. Our manager never hesitates to throw an underling under the bus when something goes wrong in the office.