Isthmus Nation refers to a nation that is connected by an isthmus, which is a narrow strip of land connecting two larger landmasses. The most famous example of an Isthmus Nation is PANAMA, which is a 6-letter word and the solution to this crossword puzzle. PANAMA is located in Central America and is bordered by Costa Rica to the west and Colombia to the east. It is known for its canal, which connects the Atlantic and Pacific Oceans.