fibula (n.)
1670s, "clasp, buckle, brooch;" 1706 as "smaller bone in the lower leg," from Latin fibula "clasp, brooch," related to figere "to fasten, fix" (see fix (v.)).

Used in reference to the outer leg bone as a loan-translation of Greek perone "small bone in the lower leg," originally "clasp, brooch; anything pointed for piercing or pinning;" the bone was so called because it resembles a clasp like a modern safety pin.