SLAVE LAKE, GREAT, a lake in the Hudson's Bay Company's territory, North America, lying between N. Lat. 60. 40. and 63.; W. Long. 109. and 117. 30. Its form is very irregular; its length from E. to W. about 250 miles, average breadth 50, area upwards of 12,000 square miles. Its northern shores are steep and rugged; and there are many rocky islands on its surface. Its largest affluent is the Slave River, from Lake Alhabasca, and it discharges its waters by the Mackenzie River into the Polar Ocean.