Hold on to (someone or something) like grim death British verb phrase
To grip, grasp or hold someone or something tightly because you do not want to lose it or fall
As soon as the branch broke off, I held on to another branch like grim death.
When the robber tried to steal my backpack, I held on to it like grim death.
To hold something tightly, as though one's life depended on it.
The verb "hold" should be conjugated according to its tense.
A problem or difficult circumstance
I'm short-sighted, so forgetting my glasses is a real hair in the butter for my sight.