To flunk is to do poorly on a test or in a class. One way to avoid flunking is to start studying several nights before a test.
People have been flunking things ever since there were schools. However, we’ve only been calling it flunking since the 1800s. Originally, flunk could mean “to fail” or “to give up.” That’s a good reminder that sometimes, to avoid flunking, you just need to keep trying.