Buckle

verb

1. To distort or collapse under physical pressure; especially, of a slender structure in compression.
2. To make bend; to cause to become distorted.
3. To give in; to react suddenly or adversely to stress or pressure (of a person).

   "It is amazing that he has never buckled after so many years of doing such urgent work."

4. To yield; to give way; to cease opposing.
5. To enter upon some labour or contest; to join in close fight; to contend.