forerunner

From Middle English forrenner, foreriner. Calque of Latin praecursor (“one who runs before, a forerunner”). Equivalent to fore- +‎ runner and/or forerun +‎ -er.

forerunner (plural forerunners)

1. A runner at the front or ahead.
2. (sports) By extension, a non-competitor who leads out the competitors on to the circuit, or who runs/rides the course prior to competitor trials, usually testing or checking the way.
3. A precursor or harbinger, a warning ahead.
   • 1922, Michael Arlen, “3/1/1”, in “Piracy”: A Romantic Chronicle of These Days‎:

     How meek and shrunken did that haughty Tarmac become as it slunk by the wide circle of asphalt of the yellow sort, that was loosely strewn before the great iron gates of Lady Hall as a forerunner of the consideration that awaited the guests of Rupert, Earl of Kare, […] .

4. A forebear, an ancestor, a predecessor.

   Bakelite is a forerunner of today's plastics.

5. (philately) A postage stamp used in the time before a region or area issues stamps of its own.

• Middle English Dictionary