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

Celsus was a veritable mint of anatomical terminology coining, or at least bringing to light, abdomen, anus, cartilage, hernia, humerus, radius, scrotum, tibia, tonsil, uterus, and vertebrae, among others (see the classic text Origin of Anatomical Terms by Henry Alan Skinner for additional information). Interestingly, Celsus was not an anatomist or even a physician but a writer who produced a compilation of Greek and Roman medical texts that became one of the most influential medical books ever written. It had been lost to history until its rediscovery in 1443 in Milan, Italy, and was part of a larger encyclopedia of general knowledge he wrote that appears gone for good.