To Buckle

1. (intransitive) To distort or collapse under physical pressure; especially, of a slender structure in compression.
2. (transitive) To make bend; to cause to become distorted.
3. (intransitive, figuratively) To give in; to react suddenly or adversely to stress or pressure (of a person).
4. (intransitive) To yield; to give way; to cease opposing.
5. (obsolete, intransitive) To enter upon some labour or contest; to join in close fight; to contend.
6. To buckle down; to apply oneself