a person who is among the first to explore or settle a country or area, especially one of the first Europeans to colonize the western US

a person who is among the first to research and develop a new area of knowledge or activity

a famous pioneer of birth control

develop or be the first to use or apply (a new method, area of knowledge, or activity)

the technique was pioneered by a Swiss doctor in the 1930s

open up (a road or terrain) as a pioneer

a series of American space probes launched between 1958 and 1973, two of which provided the first clear pictures of Jupiter and Saturn (1973–9)