fron·tier (frŭn-tîr, frŭntîr′)
a. An international border.
b. The area along an international border.
2. A region just beyond or at the edge of a settled area.
3. An undeveloped area or field for discovery or research: theories on the frontier of astrophysics.
[Middle English frountier, from Old French frontier, from front, forehead, front; see FRONT.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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