noun 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.
noun A precursor or harbinger, a warning ahead.
noun A forebear, an ancestor, a predecessor.
Bakelite is a forerunner of today's plastics.
noun A postage stamp used in the time before a region or area issues stamps of its own.