A precursor of something is a similar thing that happened or existed before it, often something which led to the existence or development of that thing.
例句
Real tennis, an ancient precursor of the modern game, originated in the eleventh century...室内网球，现代网球运动的古老前身，起源于11世纪。He said that the deal should not be seen as a precursor to a merger.他说该笔交易不应该被看作是合并的前兆。