What is the meaning of buckle?

noun

• Fastener that fastens together two ends of a belt or strap; often has loose prong.
• A shape distorted by twisting or folding.
  • synonyms: warp

verb

• Fasten with a buckle or buckles.
  • synonyms: clasp
• Fold or collapse.
  • usage: "His knees buckled"
  • synonyms: crumple
• Bend out of shape, as under pressure or from heat.
  • usage: "The highway buckled during the heat wave"
  • synonyms: heave, warp