1stumble (over/on sth) to hit your foot against sth when you are walking or running and almost fall over 绊脚;绊了一下
2stumble (over/through sth) to make a mistake when you are speaking, playing music, etc (说话、演奏等时)犯错:
The newsreader stumbled over the name of the Russian tennis player.新闻读稿员说错了那个俄罗斯网球选手的名字。
stumble across/on sb/sth to meet or find sb/sth by chance 偶遇;意外地发现