Wiktionary
forty-ninth parallel
n. 1 (context Canada US English) A nickname for the approximately 1200-mile (1900-kilometer) portion of the border between Canada and the USA, extending along the forty-ninth parallel of latitude from Lake of the Woods to the Pacific Ocean. 2 (context Canada US nonstandard English) A nickname for the entire border between Canada and the USA.
Usage examples of "forty-ninth parallel".
If he came from south of the forty-ninth parallel, he had to be an enemy.
Not until 1818 had a firm boundary been established between the United States and Canada along the forty-ninth parallel from the Rainy Lake to the Rockies.
Army has constructed temporary shelter for you in the warmer states below the forty-ninth parallel.