[buhk-uh
l] 
noun, verb, -led, -ling.| 1. | a clasp consisting of a rectangular or curved rim with one or more movable tongues, fixed to one end of a belt or strap, used for fastening to the other end of the same strap or to another strap. |
| 2. | any similar contrivance used for such purposes. |
| 3. | an ornament of metal, beads, etc., of similar appearance. |
| 4. | a bend, bulge, or kink, as in a board or saw blade. |
| 5. | to fasten with a buckle or buckles: Buckle your seat belt. |
| 6. | to shrivel, by applying heat or pressure; bend; curl. |
| 7. | to prepare (oneself) for action; apply (oneself) vigorously to something. |
| 8. | to bend, warp, or cause to give way suddenly, as with heat or pressure. |
| 9. | to close or fasten with a buckle: Grandmother always wore shoes that buckled. |
| 10. | to prepare oneself or apply oneself: The student buckled to the lesson. |
| 11. | to bend, warp, bulge, or collapse: The bridge buckled in the storm. |
| 12. | to yield, surrender, or give way to another (often fol. by under): She refused to take the medicine, but buckled under when the doctor told her to. |
| 13. | buckle down, to set to work with vigor; concentrate on one's work: He was by nature a daydreamer and found it hard to buckle down. |
| 14. | buckle up, to fasten one's belt, seat belt, or buckles: She won't start the car until we've all buckled up. |
buckle under
Give way, collapse owing to stress, as in One more heavy snowfall and the roof may buckle under, or She buckled under the strain of two jobs. [Late 1500s]