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.
Used to imply that someone is acting as if he or she is demure, innocent, sincere or reserved but they may be not
Don’t be fooled by Jennie's good behaviour. She looked as if butter wouldn't melt in her mouth.