1. To slip, stumble, and/or fall during an activity in which one is using one's feet, such as walking, dancing, climbing, etc. I sprained my ankle when I lost my footing on a hike. Be careful not to lose your footing while you're on the ladder!

2. By extension, to lose one's stability by entering a precarious or unsettling situation. I loved my job, so I really lost my footing when I was laid off. I'm just worried that he'll lose his footing if he drops out of school now—there's no guarantee he'll ever go back.