It was recorded in antiquity as Bodotria or Boderia, of unknown meaning. A 12th-century text gives it another three names, Froch, Werid and Scottewattre. Froch (for Froth) is Gaelic, which is reflected in the modern English form first appearing as Forthin in the tenth century; Werid is the British form of the same name. These forms likely derive from a British name meaning ‘slow-running one’. Scottewattre means ‘water of the Scots’ separating Scotia proper to the north from Lothian to the south.
A Norse 13th-century text refers to the Firth of Forth as Myrkvafjörðr ‘foggy firth’. In modern times the Forth is known variously in Gaelic as Abhainn Foirthe or Abhainn For, though these are possibly derived from modern English form. Its upper stretches in Stirlingshire are known however as An Abhainn Dubh ‘the black river’, running through An Gleann Dubh ‘the black glen’.
For more information on this name visit www.ainmean-aite.org