ラテン語のbucca(顎、頬)から。もともとは顎で結ぶ帽子、バックル。PIE *bheu(膨らむ、膨らむ)から。語源的にはバケツと同じ。
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]