a short piece of wood, plastic, etc. that is put through a loop of thread to fasten something, such as a coat or bag, instead of a button （大衣或口袋等上木质或塑料的）栓扣钉，棒形纽扣，套索扣 
- (also toggle switch)(
computing 计算机 a key on a computer that you press to change from one style or operation to another, and back again 转换键；切换键
Word Originmid 18th cent. (originally in nautical use): of unknown origin.