knuckle
/ˈnʌkl; `nʌkl/ n
1 bone at the finger-joint 指节; 指关节
graze/skin one's knuckles 擦破指关节. =>illus at hand 见hand插图.
2 (of animals) knee-joint, or the part joining the leg to the foot, esp as a joint of meat （指动物）膝关节, 踝; （尤指食用的）肘: pig's knuckles 猪肘.
3 (idm 习语) a rap on/over the knuckles => rap1.near the `knuckle (infml 口) on the borderline of indecency and therefore likely to offend 近乎下流; 猥亵
Some of his jokes are a bit too near the knuckle for my taste. 我觉得他有的笑话已近乎淫亵了. knuckle, v (phr v) knuckle down (to sth) (infml 口) begin to work seriously (at sth) 开始认真工作
If you want to pass that exam, you'll have to knuckle down (to some hard work). 你要想考试及格, 就得开始下功夫（苦干）了. knuckle under (infml 口) accept or admit defeat; surrender 屈服; 认输; 投降.