buck·le / ˈbəkəl/ • n. a flat, typically rectangular frame with a hinged pin, used for joining the ends of a belt or strap. ∎  a similarly shaped ornament, esp. on a shoe.• v. 1. [tr.] fasten or decorate with a buckle: he buckled his belt. ∎  [intr.] (buckle up) fasten one's seat belt in a car or aircraft.2. [intr.] bend and give way under pressure or strain: the earth buckled under the titanic stress. ∎  [tr.] bend (something) out of shape: a giant oak buckles the sidewalk. ∎ fig. (of a person) yield or collapse under pressure: a weaker person might have buckled under the strain.PHRASAL VERBS: buckle down tackle a task with determination: they will buckle down to negotiations over the next few months.

buckle sb. XIV. — (O)F. boucle metal ring, boss of a shield :- L. buccula cheek-strap of a helmet, boss of a shield, dim. of bucca cheek.
Hence buckle vb. fasten with a buckle XIV; (after F. boucler) bend under stress XVI. See -CLE.