fourfold

fourfold
/ˈfɔ:fəuld; `fɔr`fold/ adj, adv
1 four times as much or as many 四倍（的）
    The population in this area has increased fourfold. 该地区的人口已增加到四倍.
2 having four parts 有四部分（的）.

牛津英汉双解词典