knuckle

1. N-COUNT Your knuckles are the rounded pieces of bone that form lumps on your hands where your fingers join your hands, and where your fingers bend. 指关节

Brenda's knuckles were white as she gripped the arms of the chair. 布伦达紧紧抓着椅子的两个扶手时指关节白了。

2. rap sb's knuckles, rap sb on/over the knuckles→see rap