frontier (esp. American frontier)
Refers to the historical American frontier, the edge of settled land, often with a sense of adventure and expansion.
There were many dangers on the frontier during the Wild West era.
frontier (of a field); forefront (of science, technology)
Used for the cutting edge or unexplored areas of academic, scientific, or technological fields.
This research opens up a new frontier in space science.
He opened up new frontiers in genetic research.
Young scientists are taking on unknown frontiers.
Humanity is seeking a new frontier in outer space.