A FORERUNNER can a person who does something first. For example, a scientist might be a forerunner in the development of a new drug. A teacher might be a forerunner in the development of new teaching methods. A FORERUNNER can be one thing that leads to the development of another. The bicycle was a forerunner of the modern automobile. The adding machine was a forerunner of the modern computer. The word, FRONT-RUNNER, has more limited use. It describes a person in a competition who takes the lead. For example, an athlete can be a front-runner in a marathon race. One politician can be the front-runner in the leadership bids for a political party.

Hi Jayden, A "forerunner" is someone who did something first, earlier than others did something, or something that was the first general type of something that developed further into a somewhat different form later. But the focus of the word is on something happening earlier than other things. "The phonograph was the forerunner of the record player." A "frontrunner" is someone who is in the first place of some race or contest. The contest or race could have happened in the past or could be happening in the present or could happen in the future ("possible frontrunner"). The focus is on the person (or thing, I guess)'s position in this race. They are in the front of the line in the race, so they are likely to win.