Is it ensure, insure, or assure?
1520s, "foot soldier who prepares the way for the army," from Middle French pionnier "foot-soldier, pioneer," from Old French paonier "foot-soldier" (11c.), from peon (see pawn (n.2)). Figurative sense of "person who goes first or does something first" is from c.1600. Related: Pioneers.
1780, from pioneer (n.). Related: Pioneered; pioneering.