Northernmost means the farthest north of all the places or things being compared. If you're looking at a map of the United States, Alaska is the northernmost state: no other state extends as far toward the North Pole. In a row of houses on your street, the northernmost house is the one closest to the north end.

The word works like a superlative: just as “tallest” means the most tall, “northernmost” means the most north. You might read that Utqiaġvik (formerly called Barrow), Alaska, is the northernmost town in the United States, or that Norway, Sweden, and Finland compete for having the northernmost points in mainland Europe.

People use this word when location matters. Explorers historically raced to reach the northernmost point of land before the Arctic Ocean and to stand at the North Pole. Scientists study how the northernmost forests differ from southern ones because of the colder climate and shorter growing season. When you describe something as northernmost, you're giving precise geographic information: it's the extreme limit of how far north you can go in whatever region you're discussing.