Patella, directly from the Latin patella, a small dish or saucer. It is the diminutive of patera (from which we get pan). You'd think its anatomical namesake, the sesamoid bone of the quadriceps tendon also known as the kneecap, would thus shaped like a dish, but it is more triangular than round and has no concave surface. The term was introduced in its anatomical sense by Aurelius Celsus in the first century A.D.
True to its roots, an archaic name for the patella is kneepan.
A Roman patella. From the Dictionary of Greek and Roman Antiquities, by Sir William Smith, 1876