forerunner

forerunner
/ˈfɔ:rʌnə(r); `fɔrˌrʌnɚ/ n
person or thing that prepares the way for the coming of sb or sth else more important; sign of what is to follow 先驱者; 开路人; 先兆
    the forerunners of the modern diesel engine 现代柴油机的前身.

牛津英汉双解词典