What is the X in X-mas?
lower leg bone, 1726, from Latin tibia "shinbone," also "pipe, flute," in which sense it originally came into English (1540s). Of unknown origin. The Latin plural is tibiæ.
tibia tib·i·a (tĭb'ē-ə)
n. pl. tib·i·as or tib·i·ae (-ē-ē')
The inner and larger of the two bones of the lower leg, extending from the knee to the ankle, and articulating with the femur, fibula, and talus. Also called shinbone.
The larger of the two bones of the lower leg or lower portion of the hind leg. See more at skeleton.