limitrophe
/ˈlɪmɪtrəʊf/noun
A borderland; an immediately neighbouring country.
adjective
Situated on the frontier; bordering on, adjacent to (another country).
Origin
Late 16th century; earliest use found in Anthony Munday (d. 1633), playwright and translator. From (i) Middle French, French limitrophe situated on or near the frontier, (of a country) bordering on, adjacent to (another country).