Buckle

v. i.
  1. To bend permanently; to become distorted; to bow; to curl; to kink.
  2. To bend out of a true vertical plane, as a wall.
  3. To yield; to give way; to cease opposing.
  4. To enter upon some labor or contest; to join in close fight; to struggle; to contend.
    5. To buckle to ,
    to bend to; to engage with zeal.