Earn. A river and loch of South Perthshire, Scotland. The loch is 26 miles W. of Perth, and is 7 miles long by 1-1/2 wide, and is 600 feet deep, and has picturesque scenery by reason of the high mountains which surround it. The river debouches from the east end of the lake, and flows through the beautiful and fertile Strathearn into the Tay, one mile below Abernethy, after a course of 46 miles. It is navigable for 4 miles. Salmon and trout are plentiful. Bridge of Earn is four miles S.E. of Perth.