fibula
An ancient kind of brooch used to hold clothing together, similar in function to the modern safety pin.
Most of the fibulae have a triangular molding above the notch, which probably contained wound wire. The crossbar is decorated either with a flat knob or with a Persian merlon.
The smaller of the two bones in the lower leg.
Where it comes from
Borrowed from Latin fībula (“buckle, clasp, pin”). The bone is so named because the shape it makes with the tibia resembles a clasp, the fibula being the pin.
Adapted from the Wiktionary entry fibula (CC BY-SA 4.0).