Knuckles
来自Big Physics
Middle English knokel (originally denoting the rounded shape when a joint such as the elbow or knee is bent), from Middle Low German, Middle Dutch knökel, diminutive of knoke ‘bone’. In the mid 18th century the verb knuckle (down) expressed setting the knuckles down to shoot the taw in a game of marbles, hence the notion of applying oneself with concentration.
wiktionary
From knuckles.
