1. A person or group of people who were the first to do something or that leads in developing something new.
2. A person who is one of the first from another country or region to explore or settle in a new area.
3. A foot soldier whose duties include going ahead of the main company to construct things to pave the way for them.
4. The first species of plant or animal life to begin living in a previously unoccupied site; for example, a moss beginning to grow on otherwise bare rock.
5. Etymology: from 1523, "foot soldier who prepares the way for the army", from Middle French pionnier, from Old French paonier, "foot soldier" from about the 11th century from peon; from Medieval Latin pedo, pedon-, "foot soldier"; from Latin pes-, ped-, "foot".