frontero
bordering
frontier
border
+
-ero
adjective suffix
Frontero means bordering and can be thought of as frontier0 (border0) + -ero1 (adjective suffix1).
adjective
- borderingBordering or adjacent to; located at or near a borderEl pueblo frontero está en la línea divisoria entre dos países. // The bordering town is on the dividing line between two countries.