Noun:

1. a musical notation of two flats in front of a note indicating that it is to be lowered by two semitones

Double on双行靠doubleadj.双重的；成双的；两倍的v.翻一番；使 ... 加倍n.两倍；双份double pane unit双层玻璃窗double roll feed两边滚子进料double-ply bag双层袋Double - inlet双向进气double canceller二次对消器double-jointedadj.可屈曲之关节的double buffering双缓冲double objective双胶物镜double-dippingn.双津贴double telescope双筒望远镜