precursor
/ˌpriːˈkɜːsə(r)/noun
1- a person or thing that comes before another of the same kind; a forerunner前身; 先锋, 先驱：
a three-stringed precursor of the violin
小提琴的三弦前身
as modifier precursor cells.前身细胞。
1.1
- a substance from which another is formed, especially by metabolic reaction（尤指经新陈代谢形成另一种物质的）前体, 前质：
pepsinogen is the inactive precursor of pepsin.
胃蛋白酶原是胃蛋白酶的无活性前体。
词源
late Middle English: from Latin praecursor, from praecurs- 'preceded'， from praecurrere, from prae 'beforehand'+currere 'to run'.