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。
英漢詞典釋義
n.
先驅,先鋒,前身;先行者;先兆,前兆
Error is often the precursor of what is correct,but conceit is the prelude to a fall.錯誤往往是正確的先導,驕傲是跌跤的前奏。
英英詞典釋義
Noun
1. a substance from which another substance is formed (especially by a metabolic reaction)
2. a person who goes before or announces the coming of another
3. an indication of the approach of something or someone