Definitions of buckle:

• noun:   fastener that fastens together two ends of a belt or strap; often has loose prong
• noun:   a shape distorted by twisting or folding
• verb:   fold or collapse

  Example: "His knees buckled"

• verb:   fasten with a buckle or buckles
• verb:   bend out of shape, as under pressure or from heat

  Example: "The highway buckled during the heatwave"

• name:  A surname (rare: 1 in 100000 families; popularity rank in the U.S.: #17857)