The word southernmost is an adjective. Southernmost means (1) situated farthest south.
The following articles and web pages elaborate on the word southernmost.
The nation of Trinidad and Tobago occupies two islands at the southernmost end of the Eastern Caribbean chain. Learn more about these tropical islands and find travel and tourism links.
Antarctica, the southernmost continent on Earth, is home to migratory birds and penguins but no reptiles or land mammals. Very little plant life can survive in the cold, dry climate of Antarctica.
The Florida Keys have sparkling water and white sand beaches. Swimming, snorkeling, and diving are popular. Islamorada is considered the sportfishing capital of the world. Driving down the 127.5-mile Overseas Highway to Key West is an adventure. Key West, with its palm-lined streets, is the southernmost city in the continental USA. Here, Key Lime Pie is a favorite.
https://www.fla-keys.com/
The following digital image illustrates the word southernmost.