Is it ensure, insure, or assure?
"spiked metal ring for holding a belt, etc., c.1300, bukel, from Old French bocle "boss (of a shield)," then "shield," then by further extension "buckle, metal ring," (12c., Modern French boucle), from Latin buccula "cheek strap of a helmet," in Late Latin "boss of a shield," diminutive of bucca "cheek" (see bouche).
Boucle in the middle ages had the double sense of a "shield's boss" and "a ring"; the last sense has alone survived, and it metaph. developed in the boucle de cheveux, ringlets. [Kitchin]
"distort, warp, bend out of shape" 1520s, bokelen "to arch the body," from Middle French boucler "to bulge," from Old French bocler "to bulge," from bocle "boss of a shield" (see buckle (n.)). Meaning "bend under strong pressure" is from 1590s (figurative from 1640s) . Related: Buckled; buckling.
To hit; clobber (1990s+ Teenagers)
clasp or catch, particularly for fastening the ends of a belt; or a clasplike ornament, especially for shoes. The belt buckle was often used in Greece and Rome and became an indispensable part of the Teutonic warrior's equipment, as well as the object of special care on the part of metalsmiths, who ornamented many buckles with rich and intricate designs