He established that Shannon was on frontier Airlines flight 727 on June 30, 2011, from Washington to Denver.
Russian intelligence activity on the Ukrainian side of the frontier has added to that concern.
One of the rebels told us that no passports or identity papers had to be checked on this side of the frontier any longer.
c.1400, from Old French frontier "prow of a ship, front rank of an army" (13c.), noun use of adjective frontier "facing, neighboring," from front "brow" (see front (n.)).
Originally the front line of an army, sense of "borderland" is first attested early 15c. In reference to North America, from 1670s; later with a specific sense:
What is the frontier? ... In the census reports it is treated as the margin of that settlement which has a density of two or more to the square mile. [F.J. Turner, "The Frontier in American History," 1920]Frontiersman is from 1782.