properly a foot-soldier (Med. Lat. pedo, pedonis, through O. Fr. peonnier, pionnier, cf. "pawn") who with spade, axe and other implements, precedes an army or smaller military body, and clears or makes a road, digs intrenchments, prepares a camping ground, &c. The word is thus applied to all who, actually or figuratively, are first in exploring or working an undiscovered or undeveloped country or field of inquiry.