kneecap (n.)youdaoicibaDictYouDict[kneecap 词源字典]
1650s, "a covering or protection for the knee," from knee (n.) + cap (n.). Meaning "bone in front of the knee joint" is from 1869; the verb in the underworld sense of "to shoot (someone) in the knee" as punishment is attested by 1975. Related: Kneecapped.[kneecap etymology, kneecap origin, 英语词源]
popliteusyoudaoicibaDictYouDict
"A flat muscle at the back of the knee which arises from the lateral condyle of the femur and is inserted into the posterior surface of the tibia, and serves to rotate the tibia on the femur, allowing the fully extended knee to begin flexion", Late 17th cent.; earliest use found in Randle Holme (1627–1700), herald painter. From post-classical Latin popliteus, adjective (in musculus popliteus) from classical Latin poplit-, poples knee joint, back of the knee, hough, of unknown origin + -eus.