πρό-δρομος, -ον (< προτρέχω) [in LXX: Num.13:21 (20), Isa.28:4 (בִּכּוּר), Wis.12:8 * ;] running forward, going in advance. As subst., ὁ π., an advance guard, forerunner: Heb.6:20.† (AS)
Thayer:
1) a forerunner 1a) esp. one who is sent before to take observations or act as a spy, a scout, a light armed soldier 1b) one who comes in advance to a place where the rest are to follow
πρόδρομος
prodromos
prod'-rom-os
From the alternate of G4390; a runnerahead, that is, scout (figuratively precursor)