Etymology
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buckler (n.)
"small, round shield used to ward off blows," c. 1300, from Old French bocler "boss (of a shield), shield, buckler" (12c., Modern French bouclier), from Medieval Latin *buccularius (adj.) "having a boss," from Latin buccula (see buckle (n.)).
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buckle (n.)

"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]
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