the GNU version of the Collaborative International Dictionary of English
n. A valley of considerable size, through which a river runs; a valley bottom; -- often used in composition with the name of the river.
The Century Dictionary and Cyclopedia
n. In Scotland, a valley of considerable size, often having a river running through it and giving it its distinctive appellation: as, Strathspey (the valley of the Spey), Strathearn (the valley of the Earn), and Strathmore (the great valley).
Word Usage
""strath" or "dale" -- presents insurmountable philological difficulties to its identification with Gwen; the L and G, or GW not being interchangeable."