|1.||[ noun ] an international boundary or the area (often fortified) immediately inside the boundary|
|Related terms:||boundary boundary triple_frontier|
|2.||[ noun ] (geography) a wilderness at the edge of a settled area of a country|
"the individualism of the frontier in Andrew Jackson's day"
|3.||[ adjective ] on the American frontier|
"one of the last real frontier towns" "hardships of frontier life"
|4.||[ noun ] an undeveloped field of study; a topic inviting research and development|
"he worked at the frontier of brain science"