[tuō jiāng zhī mǎ]
a runaway horse -- uncontrollable; a horse that has slipped its tether; (be like) a horse without a bridle or halter; running wild; uncontrollable as a wild horse without a bridle
runaway inflation
通货膨胀如脱缰之马
Prices were running wild.
物价飞涨，有如脱缰之马。