open
closed
porous
common
Brazil has a common border with most South American countries.

disputed
northern, southern, etc.
international, national

arrive at, reach, stop at
cross, drive across, drive over, slip across, slip over
They slipped across the border at nightfall.

escape across, escape over, flee across, flee over
form, mark
A river forms the border.

draw, draw up, establish, fix
guard, patrol
open
close, seal
secure
share
Ethiopia shares its longest border with Somalia.

crossing, post
region, town
control, guard, troops
clash, dispute, war
raid
clash, incident, skirmish

across a/the border, over a/the border
to smuggle goods across the border

along a/the border
There has been fighting along the border.

at a/the border, on a/the border
We were stopped on the border.

on the border of
a farm on the border of Cumbria and Yorkshire

up to the border
He drove us right up to the Russian border.

border between, border of
the border between Austria and Switzerland

border with
the border with Mexico

north of the border, south of the border
on both sides of the border, on one side of the border
There has been fighting on both sides of the border.

wide
narrow
decorative

have
The tablecloth has a narrow lace border.

draw

with a/the border
a white handkerchief with a blue border

border around, border round (esp. BrE)
She drew a decorative border around the picture.