hold on for dear life

To hold something very tightly, as if one's life depended on it. The hiker grabbed a root as she fell off the cliff, and had to hold on for dear life while she waited for the rescue crew. When the dentist motioned us back into the examination room, my daughter clutched her chair and held on for dear life. A: "Todd's afraid of heights—how'd you get him to climb a ladder?" B: "Wait, really? Well, now I know why he's holding on for dear life!"