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...室內網球，現代網球運動的古老前身，起源于11世紀。He said that the deal should not be seen as a precursor to a merger.他說該筆交易不應該被看作是合并的前兆。