Definition of "Esk"

A river in North Yorkshire, England that flows through Eskdale to Whitby.  examples

A river in Cumbria, England, which also flows through Eskdale, and into the Irish Sea.  examples

A river in Dumfries and Galloway council area, Scotland, which crosses the border into Cumbria, England, before flowing into Solway Firth.  examples

A river mostly in East Lothian council area, Scotland, its branches North Esk and South Esk are in Midlothian.  examples